Hopf

by Chantal Roth

HTML

<!-- JSFiddle: paste EVERYTHING in this single block into the HTML panel.
     Leave the CSS + JS panels empty. -->

<style>
  html, body {
    height: 100%;
    margin: 0;
    overflow: hidden;
    background: #111;
    font-family: system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, sans-serif;
  }

  #container {
    position: fixed;
    inset: 0;
  }

  /* Info overlay */
  .overlay {
    position: fixed;
    inset: 0;
    display: grid;
    place-items: center;
    background: rgba(0, 0, 0, 0.55);
    z-index: 9999;
  }

  .hidden {
    display: none !important;
  }

  .overlay-card {
    width: min(900px, calc(100vw - 32px));
    max-height: min(80vh, 720px);
    overflow: auto;
    background: rgba(20, 20, 20, 0.98);
    border: 1px solid rgba(255, 255, 255, 0.12);
    border-radius: 12px;
    box-shadow: 0 16px 60px rgba(0, 0, 0, 0.55);
  }

  .overlay-header {
    position: sticky;
    top: 0;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 12px;
    padding: 14px 16px;
    background: rgba(28, 28, 28, 0.98);
    border-bottom: 1px solid rgba(255, 255, 255, 0.08);
  }

  .overlay-title {
    font-weight: 700;
    font-size: 16px;
    color: rgba(255, 255, 255, 0.92);
  }

  .btn {
    cursor: pointer;
    border: 1px solid rgba(255, 255, 255, 0.18);
    background: rgba(255, 255, 255, 0.06);
    color: rgba(255, 255, 255, 0.92);
    padding: 8px 12px;
    border-radius: 10px;
    font-weight: 600;
  }
  .btn:hover {
    background: rgba(255, 255, 255, 0.10);
  }

  .overlay-body {
    padding: 14px 16px 18px 16px;
    color: rgba(255, 255, 255, 0.86);
    line-height: 1.45;
    font-size: 14px;
  }

  pre.math {
    white-space: pre-wrap;
    background: rgba(255, 255, 255, 0.05);
    border: 1px solid rgba(255, 255, 255, 0.08);
    padding: 12px;
    border-radius: 10px;
    overflow: auto;
  }

  .small {
   ...