Agent File Edit Diff: CSS AI Animation

Agent File Edit Diff

An edit card for src/lib/auth.ts: two old lines blush red, three new ones push in green beneath them, and the +12 -3 counters tick up as the change lands. The counters are @property integers.

Also known as: code diff animation, file edit animation, ai code edit ui.

src/lib/auth.ts

Color Base size 16px Dark background

HTML

<div class="aia-agent-diff-card" role="status" aria-label="Editing src/lib/auth.ts">
  <div class="aia-agent-diff-card-head">
    <svg class="aia-agent-diff-card-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M14 3H7a2 2 0 0 0-2 2v14a2 2 0 0 0 2 2h10a2 2 0 0 0 2-2V8z"/><path d="M14 3v5h5"/></svg>
    <span class="aia-agent-diff-card-path">src/lib/<b>auth.ts</b></span>
    <span class="aia-agent-diff-card-add" aria-hidden="true"></span>
    <span class="aia-agent-diff-card-del" aria-hidden="true"></span>
  </div>
  <div class="aia-agent-diff-card-code" aria-hidden="true">
    <p><i>14</i><span>export async function login(req) {</span></p>
    <p class="aia-agent-diff-card-old"><i>15</i><span>  const user = await db.find(req.email);</span></p>
    <p class="aia-agent-diff-card-old"><i>16</i><span>  if (!user) throw new Error("401");</span></p>
    <div class="aia-agent-diff-card-new">
      <p><i>15</i><span>  await limiter.consume(req.ip);</span></p>
      <p><i>16</i><span>  const user = await users.byEmail(req.email);</span></p>
      <p><i>17</i><span>  if (!user) return unauthorized();</span></p>
    </div>
    <p><i>18</i><span>  return createSession(user);</span></p>
  </div>
</div>

CSS

@property --aia-agent-diff-card-a {
  syntax: "<integer>";
  inherits: false;
  initial-value: 0;
}
@property --aia-agent-diff-card-r {
  syntax: "<integer>";
  inherits: false;
  initial-value: 0;
}
.aia-agent-diff-card {
  --c: var(--aia-color, #7c5cff);
  font-size: var(--aia-size, 16px);
  font-family: system-ui, -apple-system, "Segoe UI", sans-serif;
  line-height: 1.4;
  position: relative;
  box-sizing: border-box;
  padding: 0.9em 1em;
  border-radius: 0.9em;
  background: color-mix(in srgb, currentColor 3%, transparent);
  box-shadow: inset 0 0 0 1px color-mix(in srgb, currentColor 11%, transparent), 0 0.1em 0.2em color-mix(in srgb, currentColor 4%, transparent), 0 0.9em 2em -1.1em rgb(0 0 0 / 0.3);
  --d: 7s;
  --add: color-mix(in srgb, #16a34a 78%, currentColor);
  --del: color-mix(in srgb, #dc2626 80%, currentColor);
  width: 24em;
  padding: 0;
  overflow: hidden;
}
.aia-agent-diff-card-head {
  display: flex;
  align-items: center;
  gap: 0.5em;
  padding: 0.65em 0.9em;
  border-bottom: 1px solid color-mix(in srgb, currentColor 9%, transparent);
  font-size: 0.85em;
}
.aia-agent-diff-card-icon {
  width: 1.15em;
  height: 1.15em;
  color: color-mix(in srgb, currentColor 55%, transparent);
}
.aia-agent-diff-card-path {
  margin-right: auto;
  color: color-mix(in srgb, currentColor 60%, transparent);
  font-family: ui-monospace, "SF Mono", "JetBrains Mono", Menlo, Consolas, monospace;
}
.aia-agent-diff-card-path b {
  color: currentColor;
  font-weight: 600;
}
.aia-agent-diff-card-add,
.aia-agent-diff-card-del {
  font: 600 1em ui-monospace, "SF Mono", "JetBrains Mono", Menlo, Consolas, monospace;
  font-variant-numeric: tabular-nums;
}
.aia-agent-diff-card-add {
  color: var(--add);
  counter-reset: a var(--aia-agent-diff-card-a);
  animation: aia-agent-diff-card-adds var(--d) cubic-bezier(0.4, 0, 0.2, 1) infinite;
}
.aia-agent-diff-card-add::before { content: "+" counter(a); }
.aia-agent-diff-card-del {
  color: var(--del);
  counter-reset: r var(--aia-agent-diff-card-r);
  animation: aia-agent-diff-card-dels var(--d) cubic-bezier(0.4, 0, 0.2, 1) infinite;
}
.aia-agent-diff-card-del::before { content: "-" counter(r); }
.aia-agent-diff-card-code {
  padding: 0.45em 0;
  font: 0.76em / 1 ui-monospace, "SF Mono", "JetBrains Mono", Menlo, Consolas, monospace;
  min-height: calc(1.65em * 7);
  animation: aia-agent-diff-card-fade var(--d) linear infinite;
}
.aia-agent-diff-card-code p {
  position: relative;
  display: flex;
  align-items: center;
  height: 1.65em;
  margin: 0;
  padding-right: 1em;
  white-space: pre;
  overflow: hidden;
}
.aia-agent-diff-card-code i {
  flex: none;
  width: 2.4em;
  padding-right: 1.4em;
  color: color-mix(in srgb, currentColor 35%, transparent);
  font-style: normal;
  text-align: right;
}
.aia-agent-diff-card-code p::before {
  position: absolute;
  left: 3em;
  font-weight: 700;
}
.aia-agent-diff-card-old {
  animation: aia-agent-diff-card-blush var(--d) cubic-bezier(0.4, 0, 0.2, 1) infinite;
}
.aia-agent-diff-card-old::before {
  content: "-";
  color: var(--del);
  animation: aia-agent-diff-card-mark var(--d) cubic-bezier(0.4, 0, 0.2, 1) infinite;
}
.aia-agent-diff-card-new {
  overflow: hidden;
  animation: aia-agent-diff-card-grow var(--d) cubic-bezier(0.65, 0, 0.35, 1) infinite;
}
.aia-agent-diff-card-new p {
  background: color-mix(in srgb, #16a34a 13%, transparent);
  box-shadow: inset 0.16em 0 0 var(--add);
}
.aia-agent-diff-card-new p::before {
  content: "+";
  color: var(--add);
}
@keyframes aia-agent-diff-card-blush {
  0%, 10%, 97%, 100% { background: transparent; box-shadow: none; }
  18%, 96% { background: color-mix(in srgb, #dc2626 12%, transparent); box-shadow: inset 0.16em 0 0 var(--del); }
}
@keyframes aia-agent-diff-card-mark {
  0%, 10%, 97%, 100% { opacity: 0; }
  18%, 96% { opacity: 1; }
}
@keyframes aia-agent-diff-card-grow {
  0%, 22%, 97%, 100% { height: 0; }
  48%, 96% { height: calc(1.65em * 3); }
}
@keyframes aia-agent-diff-card-adds {
  0%, 22% { --aia-agent-diff-card-a: 0; }
  48%, 90% { --aia-agent-diff-card-a: 12; opacity: 1; }
  95% { --aia-agent-diff-card-a: 12; opacity: 0; }
  97% { --aia-agent-diff-card-a: 0; opacity: 0; }
  100% { --aia-agent-diff-card-a: 0; opacity: 1; }
}
@keyframes aia-agent-diff-card-dels {
  0%, 10% { --aia-agent-diff-card-r: 0; }
  18%, 90% { --aia-agent-diff-card-r: 3; opacity: 1; }
  95% { --aia-agent-diff-card-r: 3; opacity: 0; }
  97% { --aia-agent-diff-card-r: 0; opacity: 0; }
  100% { --aia-agent-diff-card-r: 0; opacity: 1; }
}
@keyframes aia-agent-diff-card-fade {
  0%, 90% { opacity: 1; }
  95%, 97% { opacity: 0; }
  100% { opacity: 1; }
}
@media (prefers-reduced-motion: reduce) {
  .aia-agent-diff-card-add,
  .aia-agent-diff-card-del,
  .aia-agent-diff-card-code,
  .aia-agent-diff-card-old,
  .aia-agent-diff-card-old::before,
  .aia-agent-diff-card-new {
    animation-play-state: paused;
    animation-delay: calc(var(--d) * -0.7);
  }
}

@media (prefers-reduced-motion: reduce) {
  .aia-agent-diff-card, .aia-agent-diff-card *, .aia-agent-diff-card::before, .aia-agent-diff-card::after, .aia-agent-diff-card *::before, .aia-agent-diff-card *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

Customizing this snippet

Color: set --aia-color on the element or a parent. Currently previewing #3b82f6.
Base size: set --aia-size. Every other dimension is in em, so the whole thing scales together. Currently previewing 16px.
Speed: change the duration on the transition or animation shorthand. Staggered delays are relative, so they keep their rhythm.
Reduced motion: the rule at the end of the CSS turns the motion off for people who asked their OS for less of it. Keep it.

Agent File Edit Diff

HTML

CSS

Customizing this snippet

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