* { box-sizing: border-box; margin: 0; padding: 0; }
  :root {
    --bg: #f4f6f9; --card: #fff; --primary: #4a90e2; --primary-soft: #e8f1fc;
    --text: #2c3e50; --text-sub: #7b8a99; --text-muted: #aab6c2;
    --border: #eef1f5; --shadow: 0 2px 12px rgba(0,0,0,.06); --radius: 16px;
    --red: #e74c3c;
  }
  body {
    font-family: -apple-system, BlinkMacSystemFont, "PingFang SC", "Microsoft YaHei", sans-serif;
    background: var(--bg); color: var(--text); min-height: 100vh;
    display: flex; align-items: center; justify-content: center; padding: 24px;
  }
  .app { width: 100%; max-width: 1440px; }
  .card { background: var(--card); border-radius: var(--radius); box-shadow: var(--shadow); padding: 26px; }
  .header { display: flex; align-items: center; justify-content: space-between; margin-bottom: 22px; }
  .header h1 { font-size: 22px; font-weight: 600; }
  .back { font-size: 13px; color: var(--text-sub); text-decoration: none; padding: 6px 12px; background: var(--bg); border-radius: 8px; }
  .back:hover { background: var(--primary-soft); color: var(--primary); }

  /* 透明度棋盘底纹 */
  .preview-wrap {
    border-radius: 12px; margin-bottom: 18px; border: 2px solid var(--border); overflow: hidden;
    background-image: conic-gradient(#dfe4ea 0 25%, #ffffff 0 50%, #dfe4ea 0 75%, #ffffff 0);
    background-size: 22px 22px;
  }
  .preview { width: 100%; height: 90px; }

  .picker-row { display: flex; align-items: center; gap: 12px; margin-bottom: 20px; }
  .picker-row input[type="color"] { width: 56px; height: 40px; border: none; border-radius: 10px; cursor: pointer; background: none; }
  .picker-row span { font-size: 14px; color: var(--text-sub); }

  .grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0 28px; }
  @media (max-width: 760px) { .grid { grid-template-columns: 1fr; } }
  .field { margin-bottom: 14px; }
  .field label { display: block; font-size: 13px; color: var(--text-sub); margin-bottom: 6px; }
  .input-row { display: flex; gap: 8px; }
  .input-row input { flex: 1; padding: 11px 14px; border: 1.5px solid var(--border); border-radius: 10px;
    font-size: 15px; font-family: "Consolas", monospace; outline: none; background: #fafbfc; min-width: 0; }
  .input-row input:focus { border-color: var(--primary); background: #fff; }
  .input-row input.invalid { border-color: var(--red); background: #fff5f5; }
  .input-row button { padding: 0 16px; border: none; border-radius: 10px; background: var(--primary-soft);
    color: var(--primary); font-size: 13px; cursor: pointer; white-space: nowrap; }
  .input-row button:hover { opacity: .8; }

  /* alpha 滑块 */
  .alpha-row { display: flex; align-items: center; gap: 12px; }
  .alpha-row input[type="range"] { flex: 1; height: 6px; border-radius: 3px; outline: none; cursor: pointer;
    background: linear-gradient(to right, rgba(74,144,226,0), #4a90e2); }
  .alpha-row .alpha-val { width: 48px; text-align: right; font-family: "Consolas", monospace;
    font-size: 14px; color: var(--text); }

  .toast { position: fixed; bottom: 30px; left: 50%; transform: translateX(-50%) translateY(20px);
    background: var(--text); color: #fff; padding: 10px 20px; border-radius: 10px; font-size: 13px;
    opacity: 0; transition: all .3s; pointer-events: none; }
  .toast.show { opacity: 1; transform: translateX(-50%) translateY(0); }