Pulse beacon, double tap

The source

A complete HTML document. Paste it into an empty .html file and it plays — no stylesheet, script, font, or image to fetch.

<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <title>Pulse beacon — double tap</title>
    <style>
      :root {
        /* Neutrals — fixed, never remixed. */
        --ivory: #faf9f5;
        --paper: #ffffff;
        --oat: #e3dacc;
        --slate: #141413;

        /* Knobs — the remix API. A knob exists iff declared here and used below. */
        --hue: 38.8;
        --lift: 0;
        --chroma: 1;
        --speed: 1;

        /* Accents — derived from the knobs with the family's offsets baked in,
           so one hue roll moves them together. Defaults reproduce the original hex. */
        --clay: oklch(calc(0.6724 + var(--lift)) calc(0.1308 * var(--chroma)) var(--hue));
        --clay-d: oklch(calc(0.5797 + var(--lift)) calc(0.127 * var(--chroma)) var(--hue));
        --olive: oklch(
          calc(0.6118 + var(--lift)) calc(0.0713 * var(--chroma)) calc(var(--hue) + 88.3)
        );
        --rust: oklch(
          calc(0.5408 + var(--lift)) calc(0.1357 * var(--chroma)) calc(var(--hue) - 10.3)
        );

        /* Clock — every duration in the document runs off --t. The 220ms ring
           offset divides by the same --speed, which keeps the double-tap
           interval in proportion under any pace roll. */
        --cycle: 2.6s;
        --t: calc(var(--cycle) / var(--speed));
        --_offset: calc(220ms / var(--speed));

        --ease-out: cubic-bezier(0.23, 1, 0.32, 1);
      }

      * {
        box-sizing: border-box;
        margin: 0;
        padding: 0;
      }

      body {
        min-height: 100vh;
        display: grid;
        place-items: center;
        background: var(--ivory);
        font-family:
          system-ui,
          -apple-system,
          'Segoe UI',
          Roboto,
          sans-serif;
        color: var(--slate);
      }

      .status {
        display: flex;
        align-items: center;
        gap: 12px;
        font-size: 14px;
        letter-spacing: -0.01em;
      }

      .beacon {
        position: relative;
        width: 12px;
        height: 12px;
        flex: none;
      }

      .beacon span {
        position: absolute;
        inset: 0;
        border-radius: 50%;
      }

      .beacon .core {
        background: var(--olive);
      }

      /* Two rings on one cycle, offset by 220ms — a heartbeat rather than a
         metronome. The offset is the whole idea: a single ring reads as a
         clock, two read as something alive and still connected. */
      .beacon .ring {
        border: 1.5px solid var(--olive);
        opacity: 0;
        animation: beacon-double var(--t) var(--ease-out) infinite;
      }

      .beacon .ring.trailing {
        animation-delay: var(--_offset);
      }

      @keyframes beacon-double {
        0% {
          transform: scale(1);
          opacity: 0.6;
        }
        30%,
        100% {
          transform: scale(2.4);
          opacity: 0;
        }
      }

      @media (prefers-reduced-motion: reduce) {
        .beacon .ring {
          animation: beacon-double-fade var(--t) ease infinite;
          transform: scale(2);
        }

        @keyframes beacon-double-fade {
          0%,
          100% {
            opacity: 0;
          }
          15% {
            opacity: 0.45;
          }
        }
      }
    </style>
  </head>
  <body>
    <p class="status">
      <span class="beacon">
        <span class="ring"></span>
        <span class="trailing ring"></span>
        <span class="core"></span>
      </span>
      Agent connected
    </p>
  </body>
</html>

The variant family

Same idea, one axis moved. Compare them side by side before you commit.