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Pure CSSMIT licensed

Comparison Dual Timeline — Two Histories on One Spine

Two parallel stories on a shared chronological spine: company A on the left, company B on the right, year markers riding the center rail, with color-coded sides announced in headers (never color alone) — the format for rivalry retrospectives, before/after process comparisons and 'us vs the old way' marketing pages.

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The code

<section class="tls-29" aria-label="Comparison dual timeline demo">
  <div class="tls-29__inner">
    <h3 class="tls-29__title">Two roads to the same market</h3>
    <div class="tls-29__heads" aria-hidden="true"><p class="tls-29__hA">Meridian Co.</p><span></span><p class="tls-29__hB">Alto Labs</p></div>
    <ol class="tls-29__grid" role="list">
      <li class="tls-29__year" style="grid-row:1"><time datetime="2021">2021</time></li>
      <li class="tls-29__ev tls-29__ev--a" data-side="Meridian" style="grid-row:1"><h4>Raises $30M Series B</h4><p>Bets on enterprise sales and a 40-person go-to-market org.</p></li>
      <li class="tls-29__ev tls-29__ev--b" data-side="Alto" style="grid-row:1"><h4>Two founders, open beta</h4><p>Ships a free tier and answers every support email personally.</p></li>
      <li class="tls-29__year" style="grid-row:2"><time datetime="2023">2023</time></li>
      <li class="tls-29__ev tls-29__ev--a" data-side="Meridian" style="grid-row:2"><h4>500 enterprise logos</h4><p>Revenue up 4×; NPS quietly down 20 points.</p></li>
      <li class="tls-29__ev tls-29__ev--b" data-side="Alto" style="grid-row:2"><h4>100k self-serve users</h4><p>Still four people. The free tier becomes the funnel.</p></li>
      <li class="tls-29__year" style="grid-row:3"><time datetime="2026">2026</time></li>
      <li class="tls-29__ev tls-29__ev--a" data-side="Meridian" style="grid-row:3"><h4>Acquired for $400M</h4><p>The enterprise book of business was the asset.</p></li>
      <li class="tls-29__ev tls-29__ev--b" data-side="Alto" style="grid-row:3"><h4>Profitably independent</h4><p>Twelve people, no board, and the category's best-loved product.</p></li>
    </ol>
  </div>
</section>
.tls-29,
.tls-29 *,
.tls-29 *::before,
.tls-29 *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

.tls-29 {
  min-height: 100vh;
  width: 100%;
  --a: #1d4ed8;
  --b: #b45309;
  --tl-line: #e5e5e5;
  --tl-ink: #171717;
  --tl-mut: #737373;
  font-family: 'Segoe UI',system-ui,sans-serif;
  background: #fafafa;
  padding: 64px 24px;
  display: grid;
  place-items: center;
}

.tls-29__inner {
  width: min(780px,100%);
}

.tls-29__title {
  font-size: clamp(22px,3.5vw,28px);
  font-weight: 800;
  color: var(--tl-ink);
  letter-spacing: -.02em;
  text-align: center;
  margin-bottom: 26px;
}

.tls-29__heads {
  display: grid;
  grid-template-columns: 1fr 56px 1fr;
  margin-bottom: 18px;
}

.tls-29__hA,
.tls-29__hB {
  font-size: 13px;
  font-weight: 800;
  letter-spacing: .08em;
  text-transform: uppercase;
  text-align: center;
  padding: 8px 0;
  border-radius: 8px;
}

.tls-29__hA {
  color: var(--a);
  background: #eff4ff;
}

.tls-29__hB {
  color: var(--b);
  background: #fff7ea;
}

.tls-29__grid {
  list-style: none;
  display: grid;
  grid-template-columns: 1fr 56px 1fr;
  row-gap: 26px;
  position: relative;
}

.tls-29__grid::before {
  content: '';
  position: absolute;
  left: 50%;
  translate: -50% 0;
  top: -6px;
  bottom: -6px;
  width: 2px;
  background: var(--tl-line);
}

.tls-29__year {
  grid-column: 2;
  align-self: start;
  justify-self: center;
  z-index: 1;
}

.tls-29__year time {
  display: grid;
  place-items: center;
  width: 48px;
  height: 28px;
  font-size: 12.5px;
  font-weight: 800;
  color: var(--tl-ink);
  background: #fff;
  border: 2px solid var(--tl-line);
  border-radius: 999px;
}

.tls-29__ev {
  background: #fff;
  border: 1px solid var(--tl-line);
  border-radius: 14px;
  padding: 16px 18px;
}

.tls-29__ev--a {
  grid-column: 1;
  margin-right: 14px;
  border-top-right-radius: 4px;
  border-top: 3px solid var(--a);
}

.tls-29__ev--b {
  grid-column: 3;
  margin-left: 14px;
  border-top-left-radius: 4px;
  border-top: 3px solid var(--b);
}

.tls-29__ev h4 {
  font-size: 15px;
  font-weight: 750;
  color: var(--tl-ink);
  letter-spacing: -.01em;
  margin-bottom: 5px;
}

.tls-29__ev p {
  font-size: 13.5px;
  line-height: 1.55;
  color: var(--tl-mut);
  text-wrap: pretty;
}

@media (max-width: 620px) {
  .tls-29__heads {
    display: none;
  }

  .tls-29__grid {
    grid-template-columns: 1fr;
    row-gap: 14px;
  }

  .tls-29__grid::before {
    display: none;
  }

  .tls-29__year,
    .tls-29__ev--a,
    .tls-29__ev--b {
    grid-column: 1;
    grid-row: auto!important;
    margin: 0;
  }

  .tls-29__year {
    justify-self: start;
  }

  .tls-29__ev::before {
    content: attr(data-side);
    display: inline-block;
    font-size: 10px;
    font-weight: 800;
    letter-spacing: .1em;
    text-transform: uppercase;
    margin-bottom: 8px;
    padding: 2px 9px;
    border-radius: 999px;
  }

  .tls-29__ev--a::before {
    color: var(--a);
    background: #eff4ff;
  }

  .tls-29__ev--b::before {
    color: var(--b);
    background: #fff7ea;
  }
}
/* No JavaScript — paired events share an explicit grid-row across the 1fr/56px/1fr spine; the mobile collapse regenerates side labels from attr(data-side) so meaning survives the reorder. */
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 Timeline 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: Comparison Dual Timeline — Two Histories on One Spine
Source: https://codefronts.com/layouts/css-timelines/split-screen-timeline/

Two parallel stories on a shared chronological spine: company A on the left, company B on the right, year markers riding the center rail, with color-coded sides announced in headers (never color alone) — the format for rivalry retrospectives, before/after process comparisons and 'us vs the old way' marketing pages.
## HTML
```html
<section class="tls-29" aria-label="Comparison dual timeline demo">
  <div class="tls-29__inner">
    <h3 class="tls-29__title">Two roads to the same market</h3>
    <div class="tls-29__heads" aria-hidden="true"><p class="tls-29__hA">Meridian Co.</p><span></span><p class="tls-29__hB">Alto Labs</p></div>
    <ol class="tls-29__grid" role="list">
      <li class="tls-29__year" style="grid-row:1"><time datetime="2021">2021</time></li>
      <li class="tls-29__ev tls-29__ev--a" data-side="Meridian" style="grid-row:1"><h4>Raises $30M Series B</h4><p>Bets on enterprise sales and a 40-person go-to-market org.</p></li>
      <li class="tls-29__ev tls-29__ev--b" data-side="Alto" style="grid-row:1"><h4>Two founders, open beta</h4><p>Ships a free tier and answers every support email personally.</p></li>
      <li class="tls-29__year" style="grid-row:2"><time datetime="2023">2023</time></li>
      <li class="tls-29__ev tls-29__ev--a" data-side="Meridian" style="grid-row:2"><h4>500 enterprise logos</h4><p>Revenue up 4×; NPS quietly down 20 points.</p></li>
      <li class="tls-29__ev tls-29__ev--b" data-side="Alto" style="grid-row:2"><h4>100k self-serve users</h4><p>Still four people. The free tier becomes the funnel.</p></li>
      <li class="tls-29__year" style="grid-row:3"><time datetime="2026">2026</time></li>
      <li class="tls-29__ev tls-29__ev--a" data-side="Meridian" style="grid-row:3"><h4>Acquired for $400M</h4><p>The enterprise book of business was the asset.</p></li>
      <li class="tls-29__ev tls-29__ev--b" data-side="Alto" style="grid-row:3"><h4>Profitably independent</h4><p>Twelve people, no board, and the category's best-loved product.</p></li>
    </ol>
  </div>
</section>
```
## CSS
```css
.tls-29,
.tls-29 *,
.tls-29 *::before,
.tls-29 *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

.tls-29 {
  min-height: 100vh;
  width: 100%;
  --a: #1d4ed8;
  --b: #b45309;
  --tl-line: #e5e5e5;
  --tl-ink: #171717;
  --tl-mut: #737373;
  font-family: 'Segoe UI',system-ui,sans-serif;
  background: #fafafa;
  padding: 64px 24px;
  display: grid;
  place-items: center;
}

.tls-29__inner {
  width: min(780px,100%);
}

.tls-29__title {
  font-size: clamp(22px,3.5vw,28px);
  font-weight: 800;
  color: var(--tl-ink);
  letter-spacing: -.02em;
  text-align: center;
  margin-bottom: 26px;
}

.tls-29__heads {
  display: grid;
  grid-template-columns: 1fr 56px 1fr;
  margin-bottom: 18px;
}

.tls-29__hA,
.tls-29__hB {
  font-size: 13px;
  font-weight: 800;
  letter-spacing: .08em;
  text-transform: uppercase;
  text-align: center;
  padding: 8px 0;
  border-radius: 8px;
}

.tls-29__hA {
  color: var(--a);
  background: #eff4ff;
}

.tls-29__hB {
  color: var(--b);
  background: #fff7ea;
}

.tls-29__grid {
  list-style: none;
  display: grid;
  grid-template-columns: 1fr 56px 1fr;
  row-gap: 26px;
  position: relative;
}

.tls-29__grid::before {
  content: '';
  position: absolute;
  left: 50%;
  translate: -50% 0;
  top: -6px;
  bottom: -6px;
  width: 2px;
  background: var(--tl-line);
}

.tls-29__year {
  grid-column: 2;
  align-self: start;
  justify-self: center;
  z-index: 1;
}

.tls-29__year time {
  display: grid;
  place-items: center;
  width: 48px;
  height: 28px;
  font-size: 12.5px;
  font-weight: 800;
  color: var(--tl-ink);
  background: #fff;
  border: 2px solid var(--tl-line);
  border-radius: 999px;
}

.tls-29__ev {
  background: #fff;
  border: 1px solid var(--tl-line);
  border-radius: 14px;
  padding: 16px 18px;
}

.tls-29__ev--a {
  grid-column: 1;
  margin-right: 14px;
  border-top-right-radius: 4px;
  border-top: 3px solid var(--a);
}

.tls-29__ev--b {
  grid-column: 3;
  margin-left: 14px;
  border-top-left-radius: 4px;
  border-top: 3px solid var(--b);
}

.tls-29__ev h4 {
  font-size: 15px;
  font-weight: 750;
  color: var(--tl-ink);
  letter-spacing: -.01em;
  margin-bottom: 5px;
}

.tls-29__ev p {
  font-size: 13.5px;
  line-height: 1.55;
  color: var(--tl-mut);
  text-wrap: pretty;
}

@media (max-width: 620px) {
  .tls-29__heads {
    display: none;
  }

  .tls-29__grid {
    grid-template-columns: 1fr;
    row-gap: 14px;
  }

  .tls-29__grid::before {
    display: none;
  }

  .tls-29__year,
    .tls-29__ev--a,
    .tls-29__ev--b {
    grid-column: 1;
    grid-row: auto!important;
    margin: 0;
  }

  .tls-29__year {
    justify-self: start;
  }

  .tls-29__ev::before {
    content: attr(data-side);
    display: inline-block;
    font-size: 10px;
    font-weight: 800;
    letter-spacing: .1em;
    text-transform: uppercase;
    margin-bottom: 8px;
    padding: 2px 9px;
    border-radius: 999px;
  }

  .tls-29__ev--a::before {
    color: var(--a);
    background: #eff4ff;
  }

  .tls-29__ev--b::before {
    color: var(--b);
    background: #fff7ea;
  }
}
```

## JavaScript
```js
/* No JavaScript — paired events share an explicit grid-row across the 1fr/56px/1fr spine; the mobile collapse regenerates side labels from attr(data-side) so meaning survives the reorder. */
```

How this works

The spine is a three-column grid (1fr 56px 1fr) where each event picks its side with grid-column: 1 or 3 and the shared year marker occupies the center track on the SAME grid row — the crucial move is giving events and their year chip the same explicit grid-row, so a year with events on both sides aligns them shoulder-to-shoulder automatically.

Sides are declared in two ways at once: color tokens (--a blue, --b amber) AND persistent column headers naming each side, pinned above the grid. Since position is already meaning (left = A, right = B), the colors are reinforcement; a grayscale printout still reads correctly.

Cards angle toward the spine with side-specific border-radius (square inner corner) and a notch — subtle cues that each card 'belongs' to the center rail. On narrow screens a media query collapses to a single column where each card grows a side label chip (::before { content: attr(data-side) }), preserving the comparison when geometry can no longer carry it.

Techniques used: shared-spine 1fr auto 1fr grid with explicit same-row pairing · position-as-meaning + color-as-reinforcement (headers name the sides) · side-specific card chrome via square inner corners · attr(data-side) generated labels in the single-column collapse · center year chips ring-punched on the rail · semantic ol/li/time structure

Make it yours

  • Sides: rename the two headers and retint --a/--b — the layout is subject-agnostic (product vs product, plan vs plan, old vs new process).
  • Unpaired years: give an event a row of its own and leave the other side empty — the whitespace honestly shows who was quiet that year.
  • Spine width: the middle 56px track; year chips center in it automatically.
  • Collapse point: the 620px media query — tighten it if your cards run short.

Gotchas — read before shipping

  • Explicit grid-row on BOTH sides of a paired year is what aligns them — auto-placement will happily stagger rows and the comparison dissolves.
  • Don't rely on left/right alone in copy ('as shown on the left') — the mobile collapse reorders into one column; the data-side chips carry the meaning there.
  • Keep both sides' card styling identical except the accent — different chrome per side reads as editorial bias in a neutral comparison.
  • Years with events on both sides need cards of similar length, or one side dangles; trim copy rather than letting the grid gap.

Browser support

ChromeSafariFirefoxEdge
114+17.5+121+114+

Floor set by text-wrap as this demo is written. The core technique itself goes back further — Chrome all.

Grid line placement, attr() in content and media queries — baseline-everywhere CSS, nothing gated.

Techniques used in this demo

text-wrap: prettyMDN ↗role="" (ARIA)MDN ↗grid-templateMDN ↗clamp()MDN ↗place-items / place-contentMDN ↗

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