.collapsible-horizontal {
      max-width: 1400px;
      width: 100%;
      background: transparent;
      border-radius: 2rem;
    }
    .buttons-row {
      display: flex;
      flex-wrap: wrap;
      justify-content: center;
      gap: 0.85rem;
      margin-bottom: .5rem;
      row-gap: .6rem;
    }
    .collapse-btn {
      background: #2c2f33;
      border: none;
      padding: .2rem .5rem .2rem;
      font-size: 1.0rem;
      font-weight: 600;
      letter-spacing: -0.01em;
      color: #e8edf2;
      border-radius: 60px;
      cursor: pointer;
      transition: all 0.2s cubic-bezier(0.2, 0.9, 0.4, 1.1);
      box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
      font-family: inherit;
      display: inline-flex;
      align-items: center;
      gap: 0.4rem;
    }
    .collapse-btn::before {
      content: "▸";
      font-size: 1rem;
      transition: transform 0.2s ease;
      display: inline-block;
      opacity: 0.8;
    }
    .collapse-btn.active::before {
      content: "▾";
      transform: rotate(0deg);
    }

    .collapse-btn.active {
      background: #3e444a;
      color: white;
      box-shadow: 0 6px 14px rgba(0, 0, 0, 0.3);
      border: 1px solid rgba(255, 255, 255, 0.1);
    }

    .collapse-btn:hover {
      background: #3a3f44;
      transform: translateY(-2px);
    }

    .collapse-btn:active {
      transform: translateY(1px);
    }
    .panels-container {
      margin-top: 0.0rem;
      border-radius: 1.5rem;
      overflow: hidden;
    }

    .panel {
      background-color: #181a1b;
      border-radius: 1.25rem;
      margin-bottom: 0rem;
      padding: 0;
      transition: all 0.25s ease-out;
      box-shadow: 0 8px 20px rgba(0, 0, 0, 0.3);
      border: 1px solid rgba(255, 255, 255, 0.05);
    }



    /* accessibility focus ring */
    .collapse-btn:focus-visible {
      outline: 3px solid #80b0ff;
      outline-offset: 2px;
    }

    /* smooth reveal / collapse animation (height transition + slight fade) */
    .panel {
      display: block;
      overflow: hidden;
      transition: opacity 0.2s ease, transform 0.2s ease, margin 0.1s;
    }

    .panel.collapsed {
      display: none;
    }