@import url('https://fonts.googleapis.com/css2?family=Roboto+Mono:wght@500&display=swap');
  * {
    margin: 0; padding: 0; box-sizing: border-box;
  }
  body, html {
    height: 100%;
    background: linear-gradient(135deg, #0f2027, #203a43, #2c5364);
    display: flex; justify-content: center; align-items: center;
    font-family: 'Roboto Mono', monospace;
    overflow: hidden;
    user-select: none;
  }
  #gameCanvas {
    border: 2px solid #00ffea;
    /* Will apply dynamic sky color as background gradient in JS */
    box-shadow: 0 0 20px #00ffeaaa;
    display: block;
  }
  #scoreboard {
    position: fixed;
    top: 15px; left: 15px;
    color: #00ffea;
    font-size: 1.5em;
    text-shadow: 0 0 6px #00ffeaaa;
    z-index: 10;
    user-select: none;
  }
  #instructions {
    position: fixed;
    bottom: 15px; left: 15px;
    color: #00ffea88;
    font-size: 1em;
    z-index: 10;
    user-select: none;
  }
  #shopBtn {
    position: fixed;
    top: 15px; right: 15px;
    background: #00ffea33;
    border: 2px solid #00ffea;
    color: #00ffea;
    padding: 6px 12px;
    font-size: 1em;
    border-radius: 5px;
    cursor: pointer;
    z-index: 10;
    transition: background 0.3s;
    user-select: none;
  }
  #shopBtn:hover {
    background: #00ffea88;
  }
  #shopPanel {
    position: fixed;
    top: 60px; right: 15px;
    background: #003344dd;
    border: 2px solid #00ffea;
    color: #00ffea;
    padding: 15px;
    border-radius: 8px;
    width: 920px;
    max-height: 75vh;
    overflow-y: auto;
    font-size: 0.9em;
    display: none;
    z-index: 20;
    user-select: none;
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-column-gap: 10px;
  }
  #shopPanel h2 {
    grid-column: 1 / -1;
    text-align: center;
    margin-bottom: 12px;
    font-weight: 700;
    user-select: none;
  }
  .shop-column {
    padding: 0 8px;
  }
  .shop-column h3 {
    text-align: center;
    margin-bottom: 10px;
    user-select: none;
  }
  .shop-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin: 6px 0;
    border-bottom: 1px solid #00ffea44;
    padding-bottom: 6px;
  }
  .shop-item:last-child {
    border-bottom: none;
  }
  .color-swatch {
    width: 25px;
    height: 25px;
    border: 2px solid #00ffea;
    border-radius: 4px;
    cursor: pointer;
    flex-shrink: 0;
  }
  .shape-swatch {
    width: 27px;
    height: 27px;
    border: 2px solid #00ffea;
    margin: 0 4px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
  }
  .shape-swatch svg {
    width: 18px;
    height: 18px;
    fill: #00ffea;
  }
  .shop-item button {
    background: #00ffea33;
    border: 1px solid #00ffea;
    color: #00ffea;
    padding: 3px 6px;
    font-size: 0.85em;
    border-radius: 4px;
    cursor: pointer;
    transition: background 0.3s;
  }
  .shop-item button:disabled {
    opacity: 0.3;
    cursor: not-allowed;
  }
  .shop-item button:hover:not(:disabled) {
    background: #00ffea88;
  }
  #closeShopBtn {
    grid-column: 1 / -1;
    margin-top: 10px;
    padding: 6px 20px;
    background: #00ffea33;
    border: 2px solid #00ffea;
    border-radius: 6px;
    color: #00ffea;
    font-weight: 700;
    cursor: pointer;
    transition: background 0.3s;
    user-select: none;
  }
  #closeShopBtn:hover {
    background: #00ffea88;
  }
  /* Coin visual style */
  .coin-glow {
    filter: drop-shadow(0 0 3px gold);
  }