:root {
    --bg: #0d0d10;
    --panel: #18181c;
    --accent: #38bdf8;
    --font: 'Segoe UI', sans-serif;
  }
  
  body {
    background: var(--bg);
    color: #eee;
    font-family: var(--font);
    margin: 0;
    padding: 20px;
  }
  
  main {
    max-width: 1000px;
    width: 100%;
    margin: auto;
    text-align: center;
  }
  
  h1 {
    color: var(--accent);
    margin-bottom: 8px;
  }
  
  .desc {
    opacity: 0.8;
    margin-bottom: 18px;
  }
  
  .ui {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 14px;
    background: var(--panel);
    border-radius: 12px;
    padding: 12px;
    margin-bottom: 20px;
  }
  
  .control {
    display: flex;
    flex-direction: column;
    align-items: center;
    font-size: 0.9rem;
  }
  
  .control input {
    width: 160px;
  }
  
  .buttons {
    display: flex;
    flex-direction: row;
    gap: 8px;
  }
  
  button {
    background: #333;
    border: none;
    color: #eee;
    padding: 8px 14px;
    border-radius: 6px;
    cursor: pointer;
    transition: 0.2s;
  }
  button:hover { background: #444; }
  
  .simulation {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 30px;
    margin-bottom: 10px;
  }
  
  .interferometer {
    background: #111;
    padding: 10px;
    border-radius: 10px;
  }
  
  canvas {
    border: 2px solid #333;
    border-radius: 10px;
    background: black;
    max-width: 100%;
  }
  
  .readouts {
    display: flex;
    justify-content: space-around;
    margin-top: 10px;
    font-size: 0.95rem;
    opacity: 0.9;
  }
  
  #graph {
    margin-top: 20px;
    border: 2px solid #333;
    border-radius: 10px;
    background: #060606;
    width: min(100%, 800px);
    height: auto;
  }

  #fringes {
    width: min(100%, 700px);
    height: auto;
  }
  
  #theory {
    text-align: left;
    background: var(--panel);
    border-radius: 12px;
    padding: 14px 16px;
    margin-top: 20px;
  }
  #theory h2 {
    margin: 0 0 8px 0;
    color: #e2e8f0;
    font-size: 1.1rem;
  }
  #theory .facts {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 8px 16px;
    margin: 10px 0 6px 0;
    font-size: 0.95rem;
  }
  #theory .note {
    opacity: 0.85;
    font-size: 0.9rem;
    margin-top: 6px;
  }

  /* Michelson diagram + fringes: stack on narrow viewports */
  @media (max-width: 768px) {
    .simulation {
      flex-direction: column;
      gap: 16px;
    }

    .interferometer {
      width: 100%;
      max-width: 280px;
      margin-inline: auto;
      box-sizing: border-box;
    }

    #fringes {
      width: 100%;
    }
  }