20 CSS Mega Menus
03 / 20

All 20 in 20 CSS Mega Menus

  1. 01Mega Menu Reference Build with Focus Within
  2. 02Hover Intent Delay to Stop Panel Flicker
  3. 03The Safe Triangle Diagonal Pointer Problem
  4. 04Mega Menu Column Layout with CSS Grid
  5. 05Panel Positioning and Viewport Edge Collision
  6. 06Full Bleed Panel Inside a Constrained Header
  7. 07Keyboard Accessible Mega Menu with Escape
  8. 08Arrow Key Navigation Across Menu Columns
  9. 09ARIA for Disclosure Style Navigation Panels
  10. 10Mega Menu Touch and Double Tap Behavior
  11. 11Screen Reader Announcements on Panel Open
  12. 12Shared Panel That Swaps Content Between Items
  13. 13Mega Menu Entry Transition with Starting Style
  14. 14How a Mega Menu Should Collapse on Mobile
  15. 15Editorial Mega Menu with Featured Image
  16. 16Dashboard Mega Menu with Live Status Panel
  17. 17Mega Menu with Category Image Cards
  18. 18Department Store Mega Menu Grid
  19. 19Product Finder Mega Menu with Filters
  20. 20Promotional Mega Menu with Offer Panel
Light JSMIT licensed

The Safe Triangle Diagonal Pointer Problem

Moving diagonally from a nav item to the far corner of its panel passes over sibling triggers, and a naive handler closes the panel mid-journey. This fleet console tracks the pointer's trajectory and keeps the panel open while movement stays inside the triangle between the cursor and the panel's two near corners. Aim for the bottom-right link and the panel holds.

Live Demo
Plain CSSTailwind v4
Try it

Nucleo: 44,000+ SVG icons in five families · All Icons Bundle $149

Nucleo · Affiliate link

Get the Nucleo bundle

The code

<section class="mm-03" aria-labelledby="mm-03-title">
  <h2 class="mm-03__sr" id="mm-03-title">Vale Logistics operations console</h2>

  <div class="mm-03__theme">
    <input class="mm-03__theme-input" type="checkbox" id="mm-03-theme">
    <label class="mm-03__theme-label" for="mm-03-theme">
      <svg viewBox="0 0 24 24" aria-hidden="true" focusable="false"><circle cx="12" cy="12" r="8.5" fill="none" stroke="currentColor" stroke-width="1.6"/><path d="M12 3.5a8.5 8.5 0 0 0 0 17Z" fill="currentColor"/></svg>
      <span class="mm-03__sr">Toggle dark theme</span>
    </label>
  </div>

  <header class="mm-03__header" data-mm03-mode="safe" data-mm03-guard="320">
    <svg class="mm-03__viz" aria-hidden="true" focusable="false"><polygon class="mm-03__tri" points=""></polygon></svg>

    <div class="mm-03__bar">
      <a class="mm-03__brand" href="#mm-03-title">
        <svg viewBox="0 0 24 24" aria-hidden="true" focusable="false"><path d="M2 16V8h11v8Zm11-5h4l3 3.2V16h-7Z" fill="none" stroke="currentColor" stroke-width="1.7" stroke-linejoin="round"/><circle cx="7" cy="18" r="1.8" fill="currentColor"/><circle cx="17" cy="18" r="1.8" fill="currentColor"/></svg>
        Vale <span>Logistics</span>
      </a>

      <nav class="mm-03__nav" aria-label="Primary">
        <ul class="mm-03__list">
          <li class="mm-03__item">
            <button class="mm-03__trigger" type="button" aria-expanded="false" aria-controls="mm-03-panel-fleet">Fleet</button>
            <div class="mm-03__panel" id="mm-03-panel-fleet" aria-label="Fleet">
              <p class="mm-03__panel-head">Fleet operations <span>14 tools &middot; 212 depots</span></p>
              <ul class="mm-03__links">
                <li><a href="#mm-03-title"><b>Live vehicle map</b><span>realtime</span></a></li>
                <li><a href="#mm-03-title"><b>Route planner</b><span>beta</span></a></li>
                <li><a href="#mm-03-title"><b>Driver hours</b><span>compliance</span></a></li>
                <li><a href="#mm-03-title"><b>Maintenance queue</b><span>32 open</span></a></li>
                <li><a href="#mm-03-title"><b>Fuel and charging</b><span>daily</span></a></li>
                <li><a href="#mm-03-title"><b>Depot capacity</b><span>weekly</span></a></li>
                <li><a href="#mm-03-title"><b>Incident reports</b><span>archive</span></a></li>
                <li><a href="#mm-03-title"><b>Cost per mile</b><span>finance</span></a></li>
              </ul>
            </div>
          </li>

          <li class="mm-03__item">
            <button class="mm-03__trigger" type="button" aria-expanded="false" aria-controls="mm-03-panel-network">Network</button>
            <div class="mm-03__panel" id="mm-03-panel-network" aria-label="Network">
              <p class="mm-03__panel-head">Network <span>6 tools</span></p>
              <ul class="mm-03__links">
                <li><a href="#mm-03-title"><b>Depot directory</b><span>212 sites</span></a></li>
                <li><a href="#mm-03-title"><b>Partner carriers</b><span>contracts</span></a></li>
                <li><a href="#mm-03-title"><b>Coverage gaps</b><span>planning</span></a></li>
                <li><a href="#mm-03-title"><b>Service levels</b><span>SLA</span></a></li>
              </ul>
            </div>
          </li>

          <li class="mm-03__item">
            <button class="mm-03__trigger" type="button" aria-expanded="false" aria-controls="mm-03-panel-reports">Reports</button>
            <div class="mm-03__panel" id="mm-03-panel-reports" aria-label="Reports">
              <p class="mm-03__panel-head">Reports <span>9 tools</span></p>
              <ul class="mm-03__links">
                <li><a href="#mm-03-title"><b>Weekly summary</b><span>PDF</span></a></li>
                <li><a href="#mm-03-title"><b>Utilisation</b><span>dashboard</span></a></li>
                <li><a href="#mm-03-title"><b>Emissions</b><span>export</span></a></li>
                <li><a href="#mm-03-title"><b>Custom query</b><span>SQL</span></a></li>
              </ul>
            </div>
          </li>

          <li class="mm-03__item"><a class="mm-03__plain" href="#mm-03-title">Settings</a></li>
        </ul>
      </nav>

      <div class="mm-03__utils">
        <span class="mm-03__shift">Shift B &middot; 06:00&ndash;14:00</span>
        <span class="mm-03__avatar" aria-hidden="true">JL</span>
      </div>
    </div>
  </header>

  <main class="mm-03__page">
    <div class="mm-03__kpis">
      <div class="mm-03__kpi"><dt>Vehicles moving</dt><dd>1,284</dd><span>+3.1% vs yesterday</span></div>
      <div class="mm-03__kpi"><dt>On-time rate</dt><dd>96.4%</dd><span>target 95%</span></div>
      <div class="mm-03__kpi mm-03__kpi--warn"><dt>Late at depot</dt><dd>37</dd><span>18 flagged for review</span></div>
      <div class="mm-03__kpi"><dt>Cost per mile</dt><dd>&pound;1.06</dd><span>&minus;2p this week</span></div>
    </div>
  </main>
</section>
.mm-03 {
  --mm-03-bg: #17140f;
  --mm-03-surf: #211c15;
  --mm-03-panel: #f7f2e8;
  --mm-03-onpanel: #1c1710;
  --mm-03-line: #362e22;
  --mm-03-ink: #f3ede1;
  --mm-03-mut: #a3947c;
  --mm-03-acc: #f2a63b;
  --mm-03-acc: oklch(77% 0.15 70);
  --mm-03-on-acc: #12100e;
  --mm-03-panel-w: 34rem;
  --mm-03-font-display: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  width: 100%;
  min-height: 100vh;
  min-height: 100svh;
  display: block;
  position: relative;
  box-sizing: border-box;
  background-color: var(--mm-03-bg);
  background-image: radial-gradient(60rem 28rem at 82% -10%, rgba(242, 166, 59, 0.16), transparent 62%);
  color: var(--mm-03-ink);
  font-family: system-ui, -apple-system, "Segoe UI", sans-serif;
  line-height: 1.5;
}

.mm-03 *,
.mm-03 *::before,
.mm-03 *::after {
  box-sizing: border-box;
}

.mm-03 :focus-visible {
  outline: 2px solid var(--mm-03-acc);
  outline-offset: 3px;
  border-radius: 4px;
}

.mm-03__sr {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: -1px;
  padding: 0;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
  border: 0;
}

.mm-03:has(.mm-03__theme-input:checked) {
  --mm-03-bg: #f6f3ec;
  --mm-03-surf: #ffffff;
  --mm-03-panel: #1c1710;
  --mm-03-onpanel: #f7f2e8;
  --mm-03-line: #ddd4c2;
  --mm-03-ink: #1c1710;
  --mm-03-mut: #6f6455;
  --mm-03-acc: #a1560a;
  --mm-03-acc: oklch(52% 0.14 60);
  --mm-03-on-acc: #ffffff;
}

@media (prefers-color-scheme: light) {
  .mm-03 {
    --mm-03-bg: #f6f3ec;
    --mm-03-surf: #ffffff;
    --mm-03-panel: #1c1710;
    --mm-03-onpanel: #f7f2e8;
    --mm-03-line: #ddd4c2;
    --mm-03-ink: #1c1710;
    --mm-03-mut: #6f6455;
    --mm-03-acc: #a1560a;
    --mm-03-acc: oklch(52% 0.14 60);
    --mm-03-on-acc: #ffffff;
  }

  .mm-03:has(.mm-03__theme-input:checked) {
    --mm-03-bg: #17140f;
    --mm-03-surf: #211c15;
    --mm-03-panel: #f7f2e8;
    --mm-03-onpanel: #1c1710;
    --mm-03-line: #362e22;
    --mm-03-ink: #f3ede1;
    --mm-03-mut: #a3947c;
    --mm-03-acc: #f2a63b;
    --mm-03-acc: oklch(77% 0.15 70);
    --mm-03-on-acc: #12100e;
  }
}

@media (prefers-color-scheme: dark) {
  .mm-03:has(.mm-03__theme-input:checked) {
    --mm-03-bg: #f6f3ec;
    --mm-03-surf: #ffffff;
    --mm-03-panel: #1c1710;
    --mm-03-onpanel: #f7f2e8;
    --mm-03-line: #ddd4c2;
    --mm-03-ink: #1c1710;
    --mm-03-mut: #6f6455;
    --mm-03-acc: #a1560a;
    --mm-03-acc: oklch(52% 0.14 60);
    --mm-03-on-acc: #ffffff;
  }
}

.mm-03__theme {
  position: absolute;
  inset-block-start: 12px;
  inset-inline-end: clamp(0.75rem, 3vw, 1.5rem);
  z-index: 60;
}

.mm-03__theme-input {
  position: absolute;
  opacity: 0;
  inline-size: 100%;
  block-size: 100%;
  margin: 0;
  cursor: pointer;
}

.mm-03__theme-label {
  display: grid;
  place-items: center;
  inline-size: 44px;
  block-size: 44px;
  border: 1px solid var(--mm-03-line);
  border-radius: 4px;
  background: var(--mm-03-surf);
  color: var(--mm-03-ink);
  cursor: pointer;
}

.mm-03__theme-label svg {
  inline-size: 20px;
  block-size: 20px;
}

.mm-03__theme-input:focus-visible + .mm-03__theme-label {
  outline: 2px solid var(--mm-03-acc);
  outline-offset: 3px;
}

.mm-03__header {
  position: relative;
  z-index: 10;
  inline-size: 100%;
  background: var(--mm-03-surf);
  border-block-end: 1px solid var(--mm-03-line);
  padding-block-end: clamp(11rem, 26vw, 14rem);
}

.mm-03__viz {
  position: absolute;
  inset: 0;
  inline-size: 100%;
  block-size: 100%;
  pointer-events: none;
  z-index: 40;
}

.mm-03__tri {
  fill: color-mix(in oklab, var(--mm-03-acc) 20%, transparent);
  stroke: var(--mm-03-acc);
  stroke-width: 1.5;
  stroke-dasharray: 5 4;
  opacity: 0;
}

.mm-03__bar {
  inline-size: min(84rem, calc(100% - 2rem));
  margin-inline: auto;
  display: flex;
  align-items: center;
  gap: clamp(0.5rem, 2vw, 2rem);
  flex-wrap: wrap;
  min-block-size: 60px;
  padding-inline-end: 60px;
}

.mm-03__brand {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--mm-03-ink);
  text-decoration: none;
  font: 700 0.95rem/1 var(--mm-03-font-display);
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.mm-03__brand span {
  color: var(--mm-03-mut);
  font-weight: 400;
}

.mm-03__brand svg {
  inline-size: 22px;
  block-size: 22px;
  color: var(--mm-03-acc);
}

.mm-03__nav {
  min-inline-size: 0;
}

.mm-03__list {
  display: flex;
  flex-wrap: wrap;
  gap: 0.2rem;
  list-style: none;
  margin: 0;
  padding: 0;
  min-inline-size: 0;
}

.mm-03__item {
  position: relative;
}

.mm-03__trigger,
.mm-03__plain {
  display: inline-flex;
  align-items: center;
  min-block-size: 44px;
  padding-inline: 0.9rem;
  border: 0;
  border-radius: 3px;
  background: transparent;
  color: var(--mm-03-ink);
  font: 600 0.88rem/1 system-ui, sans-serif;
  text-decoration: none;
  cursor: pointer;
}

.mm-03__item--open > .mm-03__trigger,
.mm-03__item:hover > .mm-03__trigger,
.mm-03__item:focus-within > .mm-03__trigger {
  background: var(--mm-03-acc);
  color: var(--mm-03-on-acc);
}

.mm-03__plain:hover,
.mm-03__trigger:hover {
  color: var(--mm-03-acc);
}

.mm-03__utils {
  margin-inline-start: auto;
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.mm-03__shift {
  font: 500 0.72rem/1 var(--mm-03-font-display);
  letter-spacing: 0.06em;
  color: var(--mm-03-mut);
}

.mm-03__avatar {
  display: grid;
  place-items: center;
  inline-size: 32px;
  block-size: 32px;
  border-radius: 999px;
  background: color-mix(in oklab, var(--mm-03-acc) 24%, transparent);
  color: var(--mm-03-acc);
  font: 700 0.72rem/1 var(--mm-03-font-display);
}

.mm-03__panel {
  position: absolute;
  inset-block-start: 100%;
  inset-inline-start: 0;
  z-index: 30;
  inline-size: min(var(--mm-03-panel-w), calc(100vw - 3rem));
  padding: clamp(0.85rem, 2.4vw, 1.15rem);
  background: var(--mm-03-panel);
  color: var(--mm-03-onpanel);
  border-radius: 4px;
  box-shadow: 0 30px 60px -30px rgba(0, 0, 0, 0.7);
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transform: translateY(-6px);
  transition: opacity 150ms ease, transform 150ms ease, visibility 0s linear 150ms;
}

.mm-03__item--open > .mm-03__panel,
.mm-03__item:focus-within > .mm-03__panel {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
  transform: translateY(0);
  transition-delay: 0s;
}

.mm-03__panel-head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 0.75rem;
  margin: 0 0 0.6rem;
  font: 700 0.7rem/1 var(--mm-03-font-display);
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.mm-03__panel-head span {
  font-weight: 400;
  opacity: 0.6;
}

.mm-03__links {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 2px;
}

.mm-03__links a {
  display: grid;
  align-content: center;
  gap: 1px;
  min-block-size: 46px;
  padding: 0.3rem 0.55rem;
  border-radius: 3px;
  color: var(--mm-03-onpanel);
  text-decoration: none;
  min-inline-size: 0;
}

.mm-03__links b {
  font: 600 0.88rem/1.2 system-ui, sans-serif;
}

.mm-03__links span {
  font: 500 0.62rem/1 var(--mm-03-font-display);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  opacity: 0.55;
}

.mm-03__links a:hover {
  background: color-mix(in oklab, var(--mm-03-acc) 34%, transparent);
}

.mm-03__page {
  inline-size: min(84rem, calc(100% - 2rem));
  margin-inline: auto;
  padding-block: clamp(1.5rem, 5vw, 3rem);
}
/* Dividers are per-cell borders, not a 1px gap revealing the grid
   background: auto-fit leaves empty tracks at some widths and the bleed
   trick paints those as solid grey blocks. A transparent grid makes any
   item count safe. */

.mm-03__kpis {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 13rem), 1fr));
  gap: 0;
  background: transparent;
  border: 1px solid var(--mm-03-line);
  border-block-end: 0;
  border-inline-end: 0;
  border-radius: 4px;
  overflow: hidden;
}

.mm-03__kpi {
  border-inline-end: 1px solid var(--mm-03-line);
  border-block-end: 1px solid var(--mm-03-line);
  display: grid;
  gap: 2px;
  padding: 1rem 1.1rem;
  background: var(--mm-03-surf);
  min-inline-size: 0;
}

.mm-03__kpi dt {
  font: 600 0.64rem/1 var(--mm-03-font-display);
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--mm-03-mut);
}

.mm-03__kpi dd {
  margin: 0;
  font: 700 clamp(1.5rem, 4vw, 2rem)/1 var(--mm-03-font-display);
  letter-spacing: -0.02em;
  font-variant-numeric: tabular-nums;
}

.mm-03__kpi span {
  font-size: 0.74rem;
  color: var(--mm-03-mut);
}

.mm-03__kpi--warn dd {
  color: var(--mm-03-acc);
}

@media (max-width: 52rem) {
  .mm-03__header {
    padding-block-end: 0;
  }

  .mm-03__bar {
    flex-direction: column;
    align-items: stretch;
    padding-block: 0.6rem;
  }

  .mm-03__list {
    flex-direction: column;
  }

  .mm-03__utils {
    margin-inline-start: 0;
  }

  .mm-03__panel {
    position: static;
    inline-size: 100%;
    opacity: 1;
    visibility: visible;
    transform: none;
    display: none;
    margin-block-start: 0.5rem;
  }

  .mm-03__item--open > .mm-03__panel,
    .mm-03__item:focus-within > .mm-03__panel {
    display: block;
  }

  .mm-03__links {
    grid-template-columns: minmax(0, 1fr);
  }

  .mm-03__viz {
    display: none;
  }
}

@media (prefers-reduced-motion: reduce) {
  .mm-03__panel {
    transition-duration: 1ms;
  }
}
/* Panel alignment — start-aligned to its own trigger and clamped, with the panel narrowed below 60rem
   so item-left + panel-width can never exceed the bar. No ordinal flip (it pushes left-hand panels off
   the opposite edge) and no anchor position-try (the item is the containing block here, so no fallback
   can ever score better than the first). */

.mm-03__panel {
  inset-inline-start: 0;
  inset-inline-end: auto;
  max-inline-size: min(var(--mm-03-panel-w), calc(100vw - 3rem));
}

@media (max-width: 60rem) {
  .mm-03 {
    --mm-03-panel-w: 21rem;
  }
}
/* Entry signature — telemetry rows wipe open left to right on a hard linear clock */

.mm-03__links li {
  clip-path: inset(0 100% 0 0);
  opacity: 0;
  transition: clip-path 240ms linear, opacity 100ms linear;
}

.mm-03__item:hover > .mm-03__panel .mm-03__links li,
.mm-03__item:focus-within > .mm-03__panel .mm-03__links li,
.mm-03__item--open > .mm-03__panel .mm-03__links li {
  clip-path: inset(-8px);
  opacity: 1;
}

.mm-03__links li:nth-child(1) {
  transition-delay: 20ms;
}

.mm-03__links li:nth-child(2) {
  transition-delay: 60ms;
}

.mm-03__links li:nth-child(3) {
  transition-delay: 100ms;
}

.mm-03__links li:nth-child(4) {
  transition-delay: 140ms;
}

.mm-03__links li:nth-child(5) {
  transition-delay: 180ms;
}

.mm-03__links li:nth-child(6) {
  transition-delay: 220ms;
}

.mm-03__links li:nth-child(7) {
  transition-delay: 260ms;
}

.mm-03__links li:nth-child(8) {
  transition-delay: 300ms;
}

.mm-03__links li:nth-child(n+9) {
  transition-delay: 300ms;
}

@media (prefers-reduced-motion: reduce) {
  .mm-03__links li {
    transition-duration: 1ms;
    transition-delay: 0s;
    animation: none;
  }

  .mm-03__links li {
    clip-path: none;
    opacity: 1;
  }
}
const root = document.querySelector('.mm-03');
const header = root.querySelector('.mm-03__header');
const nav = root.querySelector('.mm-03__nav');
const tri = root.querySelector('.mm-03__tri');
let last = null, corners = null, guardT = 0, armed = false;
const guardMs = Number(header.dataset.mm03Guard || 320);

const setOpen = (item, on) => { item.classList.toggle('mm-03__item--open', on); item.querySelector('.mm-03__trigger').setAttribute('aria-expanded', String(on)); };
const openItem = (item) => {
  nav.querySelectorAll('.mm-03__item--open').forEach((i) => { if (i !== item) setOpen(i, false); });
  setOpen(item, true);
  const r = item.querySelector('.mm-03__panel').getBoundingClientRect();
  const h = header.getBoundingClientRect();
  corners = [[r.left - h.left, r.top - h.top], [r.right - h.left, r.top - h.top]];
};
const sign = (a, b, c) => (a[0] - c[0]) * (b[1] - c[1]) - (b[0] - c[0]) * (a[1] - c[1]);
const inside = (p) => {
  const d1 = sign(p, last, corners[0]), d2 = sign(p, corners[0], corners[1]), d3 = sign(p, corners[1], last);
  return !((d1 < 0 || d2 < 0 || d3 < 0) && (d1 > 0 || d2 > 0 || d3 > 0));
};

const onMove = (e) => {
  const h = header.getBoundingClientRect();
  const p = [e.clientX - h.left, e.clientY - h.top];
  if (header.dataset.mm03Mode === 'safe' && last && corners) {
    armed = inside(p);
    tri.setAttribute('points', last[0] + ',' + last[1] + ' ' + corners[0].join(',') + ' ' + corners[1].join(','));
    tri.style.opacity = armed ? '1' : '0';
    clearTimeout(guardT);
    guardT = setTimeout(() => { armed = false; tri.style.opacity = '0'; }, guardMs);
  }
  const item = e.target.closest('.mm-03__item');
  if (item && item.querySelector('.mm-03__panel') && !armed && !item.classList.contains('mm-03__item--open')) openItem(item);
  last = p;
};
const onKey = (e) => {
  if (e.key !== 'Escape') return;
  const open = nav.querySelector('.mm-03__item--open');
  if (!open) return;
  setOpen(open, false); open.querySelector('.mm-03__trigger').focus();
};
const onResize = () => { const open = nav.querySelector('.mm-03__item--open'); if (open) openItem(open); };

// Nothing closed the panel on the way out — only Escape did — so leaving
// the header left it open indefinitely. Close when the pointer genuinely
// leaves the header, keeping it open while focus is still inside.
const onLeave = (e) => {
  if (e.relatedTarget && header.contains(e.relatedTarget)) return;
  if (header.contains(document.activeElement)) return;
  clearTimeout(guardT); armed = false; last = null; tri.style.opacity = '0';
  nav.querySelectorAll('.mm-03__item--open').forEach((i) => setOpen(i, false));
};

header.addEventListener('pointermove', onMove);
header.addEventListener('pointerleave', onLeave);
nav.addEventListener('keydown', onKey);
window.addEventListener('resize', onResize);

root.__mmCleanup = () => {
  header.removeEventListener('pointermove', onMove);
  header.removeEventListener('pointerleave', onLeave);
  nav.removeEventListener('keydown', onKey);
  window.removeEventListener('resize', onResize);
  clearTimeout(guardT);
};
Paste this into ChatGPT, Claude, Cursor, or any coding assistant. The block below is pre-framed with everything the AI needs to integrate this demo into your project — markup, styles, scoping notes, and the source URL. Hit Copy and paste straight into your chat.
Here's a working CSS Mega Menu from CodeFronts. Use it as-is or adapt to your framework. All classes are scoped under a unique prefix so the code won't collide with your existing styles. MIT licensed.
Demo: The Safe Triangle Diagonal Pointer Problem
Source: https://codefronts.com/navigation/css-mega-menus/the-safe-triangle-diagonal-pointer-problem/

Moving diagonally from a nav item to the far corner of its panel passes over sibling triggers, and a naive handler closes the panel mid-journey. This fleet console tracks the pointer's trajectory and keeps the panel open while movement stays inside the triangle between the cursor and the panel's two near corners. Aim for the bottom-right link and the panel holds.
## HTML
```html
<section class="mm-03" aria-labelledby="mm-03-title">
  <h2 class="mm-03__sr" id="mm-03-title">Vale Logistics operations console</h2>

  <div class="mm-03__theme">
    <input class="mm-03__theme-input" type="checkbox" id="mm-03-theme">
    <label class="mm-03__theme-label" for="mm-03-theme">
      <svg viewBox="0 0 24 24" aria-hidden="true" focusable="false"><circle cx="12" cy="12" r="8.5" fill="none" stroke="currentColor" stroke-width="1.6"/><path d="M12 3.5a8.5 8.5 0 0 0 0 17Z" fill="currentColor"/></svg>
      <span class="mm-03__sr">Toggle dark theme</span>
    </label>
  </div>

  <header class="mm-03__header" data-mm03-mode="safe" data-mm03-guard="320">
    <svg class="mm-03__viz" aria-hidden="true" focusable="false"><polygon class="mm-03__tri" points=""></polygon></svg>

    <div class="mm-03__bar">
      <a class="mm-03__brand" href="#mm-03-title">
        <svg viewBox="0 0 24 24" aria-hidden="true" focusable="false"><path d="M2 16V8h11v8Zm11-5h4l3 3.2V16h-7Z" fill="none" stroke="currentColor" stroke-width="1.7" stroke-linejoin="round"/><circle cx="7" cy="18" r="1.8" fill="currentColor"/><circle cx="17" cy="18" r="1.8" fill="currentColor"/></svg>
        Vale <span>Logistics</span>
      </a>

      <nav class="mm-03__nav" aria-label="Primary">
        <ul class="mm-03__list">
          <li class="mm-03__item">
            <button class="mm-03__trigger" type="button" aria-expanded="false" aria-controls="mm-03-panel-fleet">Fleet</button>
            <div class="mm-03__panel" id="mm-03-panel-fleet" aria-label="Fleet">
              <p class="mm-03__panel-head">Fleet operations <span>14 tools &middot; 212 depots</span></p>
              <ul class="mm-03__links">
                <li><a href="#mm-03-title"><b>Live vehicle map</b><span>realtime</span></a></li>
                <li><a href="#mm-03-title"><b>Route planner</b><span>beta</span></a></li>
                <li><a href="#mm-03-title"><b>Driver hours</b><span>compliance</span></a></li>
                <li><a href="#mm-03-title"><b>Maintenance queue</b><span>32 open</span></a></li>
                <li><a href="#mm-03-title"><b>Fuel and charging</b><span>daily</span></a></li>
                <li><a href="#mm-03-title"><b>Depot capacity</b><span>weekly</span></a></li>
                <li><a href="#mm-03-title"><b>Incident reports</b><span>archive</span></a></li>
                <li><a href="#mm-03-title"><b>Cost per mile</b><span>finance</span></a></li>
              </ul>
            </div>
          </li>

          <li class="mm-03__item">
            <button class="mm-03__trigger" type="button" aria-expanded="false" aria-controls="mm-03-panel-network">Network</button>
            <div class="mm-03__panel" id="mm-03-panel-network" aria-label="Network">
              <p class="mm-03__panel-head">Network <span>6 tools</span></p>
              <ul class="mm-03__links">
                <li><a href="#mm-03-title"><b>Depot directory</b><span>212 sites</span></a></li>
                <li><a href="#mm-03-title"><b>Partner carriers</b><span>contracts</span></a></li>
                <li><a href="#mm-03-title"><b>Coverage gaps</b><span>planning</span></a></li>
                <li><a href="#mm-03-title"><b>Service levels</b><span>SLA</span></a></li>
              </ul>
            </div>
          </li>

          <li class="mm-03__item">
            <button class="mm-03__trigger" type="button" aria-expanded="false" aria-controls="mm-03-panel-reports">Reports</button>
            <div class="mm-03__panel" id="mm-03-panel-reports" aria-label="Reports">
              <p class="mm-03__panel-head">Reports <span>9 tools</span></p>
              <ul class="mm-03__links">
                <li><a href="#mm-03-title"><b>Weekly summary</b><span>PDF</span></a></li>
                <li><a href="#mm-03-title"><b>Utilisation</b><span>dashboard</span></a></li>
                <li><a href="#mm-03-title"><b>Emissions</b><span>export</span></a></li>
                <li><a href="#mm-03-title"><b>Custom query</b><span>SQL</span></a></li>
              </ul>
            </div>
          </li>

          <li class="mm-03__item"><a class="mm-03__plain" href="#mm-03-title">Settings</a></li>
        </ul>
      </nav>

      <div class="mm-03__utils">
        <span class="mm-03__shift">Shift B &middot; 06:00&ndash;14:00</span>
        <span class="mm-03__avatar" aria-hidden="true">JL</span>
      </div>
    </div>
  </header>

  <main class="mm-03__page">
    <div class="mm-03__kpis">
      <div class="mm-03__kpi"><dt>Vehicles moving</dt><dd>1,284</dd><span>+3.1% vs yesterday</span></div>
      <div class="mm-03__kpi"><dt>On-time rate</dt><dd>96.4%</dd><span>target 95%</span></div>
      <div class="mm-03__kpi mm-03__kpi--warn"><dt>Late at depot</dt><dd>37</dd><span>18 flagged for review</span></div>
      <div class="mm-03__kpi"><dt>Cost per mile</dt><dd>&pound;1.06</dd><span>&minus;2p this week</span></div>
    </div>
  </main>
</section>
```
## CSS
```css
.mm-03 {
  --mm-03-bg: #17140f;
  --mm-03-surf: #211c15;
  --mm-03-panel: #f7f2e8;
  --mm-03-onpanel: #1c1710;
  --mm-03-line: #362e22;
  --mm-03-ink: #f3ede1;
  --mm-03-mut: #a3947c;
  --mm-03-acc: #f2a63b;
  --mm-03-acc: oklch(77% 0.15 70);
  --mm-03-on-acc: #12100e;
  --mm-03-panel-w: 34rem;
  --mm-03-font-display: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  width: 100%;
  min-height: 100vh;
  min-height: 100svh;
  display: block;
  position: relative;
  box-sizing: border-box;
  background-color: var(--mm-03-bg);
  background-image: radial-gradient(60rem 28rem at 82% -10%, rgba(242, 166, 59, 0.16), transparent 62%);
  color: var(--mm-03-ink);
  font-family: system-ui, -apple-system, "Segoe UI", sans-serif;
  line-height: 1.5;
}

.mm-03 *,
.mm-03 *::before,
.mm-03 *::after {
  box-sizing: border-box;
}

.mm-03 :focus-visible {
  outline: 2px solid var(--mm-03-acc);
  outline-offset: 3px;
  border-radius: 4px;
}

.mm-03__sr {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: -1px;
  padding: 0;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
  border: 0;
}

.mm-03:has(.mm-03__theme-input:checked) {
  --mm-03-bg: #f6f3ec;
  --mm-03-surf: #ffffff;
  --mm-03-panel: #1c1710;
  --mm-03-onpanel: #f7f2e8;
  --mm-03-line: #ddd4c2;
  --mm-03-ink: #1c1710;
  --mm-03-mut: #6f6455;
  --mm-03-acc: #a1560a;
  --mm-03-acc: oklch(52% 0.14 60);
  --mm-03-on-acc: #ffffff;
}

@media (prefers-color-scheme: light) {
  .mm-03 {
    --mm-03-bg: #f6f3ec;
    --mm-03-surf: #ffffff;
    --mm-03-panel: #1c1710;
    --mm-03-onpanel: #f7f2e8;
    --mm-03-line: #ddd4c2;
    --mm-03-ink: #1c1710;
    --mm-03-mut: #6f6455;
    --mm-03-acc: #a1560a;
    --mm-03-acc: oklch(52% 0.14 60);
    --mm-03-on-acc: #ffffff;
  }

  .mm-03:has(.mm-03__theme-input:checked) {
    --mm-03-bg: #17140f;
    --mm-03-surf: #211c15;
    --mm-03-panel: #f7f2e8;
    --mm-03-onpanel: #1c1710;
    --mm-03-line: #362e22;
    --mm-03-ink: #f3ede1;
    --mm-03-mut: #a3947c;
    --mm-03-acc: #f2a63b;
    --mm-03-acc: oklch(77% 0.15 70);
    --mm-03-on-acc: #12100e;
  }
}

@media (prefers-color-scheme: dark) {
  .mm-03:has(.mm-03__theme-input:checked) {
    --mm-03-bg: #f6f3ec;
    --mm-03-surf: #ffffff;
    --mm-03-panel: #1c1710;
    --mm-03-onpanel: #f7f2e8;
    --mm-03-line: #ddd4c2;
    --mm-03-ink: #1c1710;
    --mm-03-mut: #6f6455;
    --mm-03-acc: #a1560a;
    --mm-03-acc: oklch(52% 0.14 60);
    --mm-03-on-acc: #ffffff;
  }
}

.mm-03__theme {
  position: absolute;
  inset-block-start: 12px;
  inset-inline-end: clamp(0.75rem, 3vw, 1.5rem);
  z-index: 60;
}

.mm-03__theme-input {
  position: absolute;
  opacity: 0;
  inline-size: 100%;
  block-size: 100%;
  margin: 0;
  cursor: pointer;
}

.mm-03__theme-label {
  display: grid;
  place-items: center;
  inline-size: 44px;
  block-size: 44px;
  border: 1px solid var(--mm-03-line);
  border-radius: 4px;
  background: var(--mm-03-surf);
  color: var(--mm-03-ink);
  cursor: pointer;
}

.mm-03__theme-label svg {
  inline-size: 20px;
  block-size: 20px;
}

.mm-03__theme-input:focus-visible + .mm-03__theme-label {
  outline: 2px solid var(--mm-03-acc);
  outline-offset: 3px;
}

.mm-03__header {
  position: relative;
  z-index: 10;
  inline-size: 100%;
  background: var(--mm-03-surf);
  border-block-end: 1px solid var(--mm-03-line);
  padding-block-end: clamp(11rem, 26vw, 14rem);
}

.mm-03__viz {
  position: absolute;
  inset: 0;
  inline-size: 100%;
  block-size: 100%;
  pointer-events: none;
  z-index: 40;
}

.mm-03__tri {
  fill: color-mix(in oklab, var(--mm-03-acc) 20%, transparent);
  stroke: var(--mm-03-acc);
  stroke-width: 1.5;
  stroke-dasharray: 5 4;
  opacity: 0;
}

.mm-03__bar {
  inline-size: min(84rem, calc(100% - 2rem));
  margin-inline: auto;
  display: flex;
  align-items: center;
  gap: clamp(0.5rem, 2vw, 2rem);
  flex-wrap: wrap;
  min-block-size: 60px;
  padding-inline-end: 60px;
}

.mm-03__brand {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--mm-03-ink);
  text-decoration: none;
  font: 700 0.95rem/1 var(--mm-03-font-display);
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.mm-03__brand span {
  color: var(--mm-03-mut);
  font-weight: 400;
}

.mm-03__brand svg {
  inline-size: 22px;
  block-size: 22px;
  color: var(--mm-03-acc);
}

.mm-03__nav {
  min-inline-size: 0;
}

.mm-03__list {
  display: flex;
  flex-wrap: wrap;
  gap: 0.2rem;
  list-style: none;
  margin: 0;
  padding: 0;
  min-inline-size: 0;
}

.mm-03__item {
  position: relative;
}

.mm-03__trigger,
.mm-03__plain {
  display: inline-flex;
  align-items: center;
  min-block-size: 44px;
  padding-inline: 0.9rem;
  border: 0;
  border-radius: 3px;
  background: transparent;
  color: var(--mm-03-ink);
  font: 600 0.88rem/1 system-ui, sans-serif;
  text-decoration: none;
  cursor: pointer;
}

.mm-03__item--open > .mm-03__trigger,
.mm-03__item:hover > .mm-03__trigger,
.mm-03__item:focus-within > .mm-03__trigger {
  background: var(--mm-03-acc);
  color: var(--mm-03-on-acc);
}

.mm-03__plain:hover,
.mm-03__trigger:hover {
  color: var(--mm-03-acc);
}

.mm-03__utils {
  margin-inline-start: auto;
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.mm-03__shift {
  font: 500 0.72rem/1 var(--mm-03-font-display);
  letter-spacing: 0.06em;
  color: var(--mm-03-mut);
}

.mm-03__avatar {
  display: grid;
  place-items: center;
  inline-size: 32px;
  block-size: 32px;
  border-radius: 999px;
  background: color-mix(in oklab, var(--mm-03-acc) 24%, transparent);
  color: var(--mm-03-acc);
  font: 700 0.72rem/1 var(--mm-03-font-display);
}

.mm-03__panel {
  position: absolute;
  inset-block-start: 100%;
  inset-inline-start: 0;
  z-index: 30;
  inline-size: min(var(--mm-03-panel-w), calc(100vw - 3rem));
  padding: clamp(0.85rem, 2.4vw, 1.15rem);
  background: var(--mm-03-panel);
  color: var(--mm-03-onpanel);
  border-radius: 4px;
  box-shadow: 0 30px 60px -30px rgba(0, 0, 0, 0.7);
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transform: translateY(-6px);
  transition: opacity 150ms ease, transform 150ms ease, visibility 0s linear 150ms;
}

.mm-03__item--open > .mm-03__panel,
.mm-03__item:focus-within > .mm-03__panel {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
  transform: translateY(0);
  transition-delay: 0s;
}

.mm-03__panel-head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 0.75rem;
  margin: 0 0 0.6rem;
  font: 700 0.7rem/1 var(--mm-03-font-display);
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.mm-03__panel-head span {
  font-weight: 400;
  opacity: 0.6;
}

.mm-03__links {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 2px;
}

.mm-03__links a {
  display: grid;
  align-content: center;
  gap: 1px;
  min-block-size: 46px;
  padding: 0.3rem 0.55rem;
  border-radius: 3px;
  color: var(--mm-03-onpanel);
  text-decoration: none;
  min-inline-size: 0;
}

.mm-03__links b {
  font: 600 0.88rem/1.2 system-ui, sans-serif;
}

.mm-03__links span {
  font: 500 0.62rem/1 var(--mm-03-font-display);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  opacity: 0.55;
}

.mm-03__links a:hover {
  background: color-mix(in oklab, var(--mm-03-acc) 34%, transparent);
}

.mm-03__page {
  inline-size: min(84rem, calc(100% - 2rem));
  margin-inline: auto;
  padding-block: clamp(1.5rem, 5vw, 3rem);
}
/* Dividers are per-cell borders, not a 1px gap revealing the grid
   background: auto-fit leaves empty tracks at some widths and the bleed
   trick paints those as solid grey blocks. A transparent grid makes any
   item count safe. */

.mm-03__kpis {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 13rem), 1fr));
  gap: 0;
  background: transparent;
  border: 1px solid var(--mm-03-line);
  border-block-end: 0;
  border-inline-end: 0;
  border-radius: 4px;
  overflow: hidden;
}

.mm-03__kpi {
  border-inline-end: 1px solid var(--mm-03-line);
  border-block-end: 1px solid var(--mm-03-line);
  display: grid;
  gap: 2px;
  padding: 1rem 1.1rem;
  background: var(--mm-03-surf);
  min-inline-size: 0;
}

.mm-03__kpi dt {
  font: 600 0.64rem/1 var(--mm-03-font-display);
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--mm-03-mut);
}

.mm-03__kpi dd {
  margin: 0;
  font: 700 clamp(1.5rem, 4vw, 2rem)/1 var(--mm-03-font-display);
  letter-spacing: -0.02em;
  font-variant-numeric: tabular-nums;
}

.mm-03__kpi span {
  font-size: 0.74rem;
  color: var(--mm-03-mut);
}

.mm-03__kpi--warn dd {
  color: var(--mm-03-acc);
}

@media (max-width: 52rem) {
  .mm-03__header {
    padding-block-end: 0;
  }

  .mm-03__bar {
    flex-direction: column;
    align-items: stretch;
    padding-block: 0.6rem;
  }

  .mm-03__list {
    flex-direction: column;
  }

  .mm-03__utils {
    margin-inline-start: 0;
  }

  .mm-03__panel {
    position: static;
    inline-size: 100%;
    opacity: 1;
    visibility: visible;
    transform: none;
    display: none;
    margin-block-start: 0.5rem;
  }

  .mm-03__item--open > .mm-03__panel,
    .mm-03__item:focus-within > .mm-03__panel {
    display: block;
  }

  .mm-03__links {
    grid-template-columns: minmax(0, 1fr);
  }

  .mm-03__viz {
    display: none;
  }
}

@media (prefers-reduced-motion: reduce) {
  .mm-03__panel {
    transition-duration: 1ms;
  }
}
/* Panel alignment — start-aligned to its own trigger and clamped, with the panel narrowed below 60rem
   so item-left + panel-width can never exceed the bar. No ordinal flip (it pushes left-hand panels off
   the opposite edge) and no anchor position-try (the item is the containing block here, so no fallback
   can ever score better than the first). */

.mm-03__panel {
  inset-inline-start: 0;
  inset-inline-end: auto;
  max-inline-size: min(var(--mm-03-panel-w), calc(100vw - 3rem));
}

@media (max-width: 60rem) {
  .mm-03 {
    --mm-03-panel-w: 21rem;
  }
}
/* Entry signature — telemetry rows wipe open left to right on a hard linear clock */

.mm-03__links li {
  clip-path: inset(0 100% 0 0);
  opacity: 0;
  transition: clip-path 240ms linear, opacity 100ms linear;
}

.mm-03__item:hover > .mm-03__panel .mm-03__links li,
.mm-03__item:focus-within > .mm-03__panel .mm-03__links li,
.mm-03__item--open > .mm-03__panel .mm-03__links li {
  clip-path: inset(-8px);
  opacity: 1;
}

.mm-03__links li:nth-child(1) {
  transition-delay: 20ms;
}

.mm-03__links li:nth-child(2) {
  transition-delay: 60ms;
}

.mm-03__links li:nth-child(3) {
  transition-delay: 100ms;
}

.mm-03__links li:nth-child(4) {
  transition-delay: 140ms;
}

.mm-03__links li:nth-child(5) {
  transition-delay: 180ms;
}

.mm-03__links li:nth-child(6) {
  transition-delay: 220ms;
}

.mm-03__links li:nth-child(7) {
  transition-delay: 260ms;
}

.mm-03__links li:nth-child(8) {
  transition-delay: 300ms;
}

.mm-03__links li:nth-child(n+9) {
  transition-delay: 300ms;
}

@media (prefers-reduced-motion: reduce) {
  .mm-03__links li {
    transition-duration: 1ms;
    transition-delay: 0s;
    animation: none;
  }

  .mm-03__links li {
    clip-path: none;
    opacity: 1;
  }
}
```

## JavaScript
```js
const root = document.querySelector('.mm-03');
const header = root.querySelector('.mm-03__header');
const nav = root.querySelector('.mm-03__nav');
const tri = root.querySelector('.mm-03__tri');
let last = null, corners = null, guardT = 0, armed = false;
const guardMs = Number(header.dataset.mm03Guard || 320);

const setOpen = (item, on) => { item.classList.toggle('mm-03__item--open', on); item.querySelector('.mm-03__trigger').setAttribute('aria-expanded', String(on)); };
const openItem = (item) => {
  nav.querySelectorAll('.mm-03__item--open').forEach((i) => { if (i !== item) setOpen(i, false); });
  setOpen(item, true);
  const r = item.querySelector('.mm-03__panel').getBoundingClientRect();
  const h = header.getBoundingClientRect();
  corners = [[r.left - h.left, r.top - h.top], [r.right - h.left, r.top - h.top]];
};
const sign = (a, b, c) => (a[0] - c[0]) * (b[1] - c[1]) - (b[0] - c[0]) * (a[1] - c[1]);
const inside = (p) => {
  const d1 = sign(p, last, corners[0]), d2 = sign(p, corners[0], corners[1]), d3 = sign(p, corners[1], last);
  return !((d1 < 0 || d2 < 0 || d3 < 0) && (d1 > 0 || d2 > 0 || d3 > 0));
};

const onMove = (e) => {
  const h = header.getBoundingClientRect();
  const p = [e.clientX - h.left, e.clientY - h.top];
  if (header.dataset.mm03Mode === 'safe' && last && corners) {
    armed = inside(p);
    tri.setAttribute('points', last[0] + ',' + last[1] + ' ' + corners[0].join(',') + ' ' + corners[1].join(','));
    tri.style.opacity = armed ? '1' : '0';
    clearTimeout(guardT);
    guardT = setTimeout(() => { armed = false; tri.style.opacity = '0'; }, guardMs);
  }
  const item = e.target.closest('.mm-03__item');
  if (item && item.querySelector('.mm-03__panel') && !armed && !item.classList.contains('mm-03__item--open')) openItem(item);
  last = p;
};
const onKey = (e) => {
  if (e.key !== 'Escape') return;
  const open = nav.querySelector('.mm-03__item--open');
  if (!open) return;
  setOpen(open, false); open.querySelector('.mm-03__trigger').focus();
};
const onResize = () => { const open = nav.querySelector('.mm-03__item--open'); if (open) openItem(open); };

// Nothing closed the panel on the way out — only Escape did — so leaving
// the header left it open indefinitely. Close when the pointer genuinely
// leaves the header, keeping it open while focus is still inside.
const onLeave = (e) => {
  if (e.relatedTarget && header.contains(e.relatedTarget)) return;
  if (header.contains(document.activeElement)) return;
  clearTimeout(guardT); armed = false; last = null; tri.style.opacity = '0';
  nav.querySelectorAll('.mm-03__item--open').forEach((i) => setOpen(i, false));
};

header.addEventListener('pointermove', onMove);
header.addEventListener('pointerleave', onLeave);
nav.addEventListener('keydown', onKey);
window.addEventListener('resize', onResize);

root.__mmCleanup = () => {
  header.removeEventListener('pointermove', onMove);
  header.removeEventListener('pointerleave', onLeave);
  nav.removeEventListener('keydown', onKey);
  window.removeEventListener('resize', onResize);
  clearTimeout(guardT);
};
```

How this works

The bug is geometric, not temporal. A panel is wider than its trigger, so the shortest path from the trigger to a link in the panel's far corner is a diagonal, and that diagonal crosses the trigger next door. The sibling fires its own open, the first panel closes, and the link the user was aiming at moves out from under the cursor. A close delay does not help here, because the pointer is genuinely sitting on a different trigger by then, not in dead space.

The fix asks where the pointer is going, not where it is. When a panel opens, record its top-left and top-right corners. On every pointermove, form a triangle from the previous pointer position to those two corners. If the current position falls inside that triangle, the user is travelling toward the panel, so ignore whatever they are hovering over and keep the panel open. If they fall outside it, they have changed their mind and the sibling is allowed to take over.

The test itself is three sign checks. For each edge of the triangle, compute the cross product of the edge vector with the vector to the point; if all three have the same sign, the point is inside. That runs on a pointermove and never touches layout — the corner rectangle is cached at open time, so no read forces a reflow mid-gesture.

Do not reach for this first. A generous close delay from demo 02 solves the same complaint in ten lines whenever the panel sits directly below its trigger and the gap is small. The safe triangle earns its complexity in two cases: side-opening submenus, where the diagonal is unavoidable, and very wide panels whose far corner is a long way from the trigger. If your panel is full-bleed and starts immediately below the bar, ship the delay and move on.

Make it yours

  • Change data-mm03-guard on the header to lengthen how long the triangle stays armed after the last move.
  • Set data-mm03-mode to naive to disable the guard and feel the original problem.
  • Widen the panel with --mm-03-panel-w to make the diagonal longer and the guard more valuable.
  • Swap the triangle apex from the previous pointer position to the trigger's centre for a fixed, simpler guard.
  • Change the two-up link grid to three columns by editing one repeat() in .mm-03__links.
  • Recolour with the two --mm-03-acc declarations, hex first then oklch.

Gotchas — read before shipping

  • Building the triangle from the current pointer position instead of the previous one gives a degenerate zero-area triangle that never matches. The apex must be where the pointer was, not where it is.
  • Reading getBoundingClientRect() inside the pointermove handler forces layout on every sample and turns a smooth gesture into jank. Cache the corners when the panel opens.
  • The guard must expire. If the pointer stops inside the triangle and stays there, an unexpiring guard means a sibling trigger can never open, which reads as a dead nav bar.
  • Nothing about this helps keyboard or touch users, and it must never be the only way to reach a panel. Focus and click paths stay independent of the geometry.
  • Leaving the pointermove listener attached after unmount keeps sampling against detached rectangles. The cleanup removes it along with the resize listener.

Browser support

ChromeSafariFirefoxEdge
111+15.4+121+111+

oklch() and the :has() theme toggle set the floor. Pointer events, getBoundingClientRect and the cross-product test are decade-old APIs, so the guard itself imposes nothing; below the oklch() floor the sRGB hex declared first applies and if :has() is missing the toggle stops switching while the panel still works.

Techniques used in this demo

:focus-withinMDN ↗clip-pathMDN ↗:has()MDN ↗radial-gradient()MDN ↗grid-templateMDN ↗color-mix()MDN ↗

Search CodeFronts

Loading…

↑↓ navigate↵ selectesc closeOpen full search page →