:root {
      --color-background: #0a0a0a;
      --color-surface: #111111;
      --color-surface-elevated: #1a1a1a;
      --color-surface-hover: #1e1e1e;
      --color-primary: #ffffff;
      --color-primary-hover: #f0f0f0;
      --color-accent: #3b82f6;
      --color-accent-hover: #2563eb;
      --color-stroke: #2a2a2a;
      --color-stroke-subtle: #1f1f1f;
      --color-text-primary: #ffffff;
      --color-text-secondary: #a1a1a1;
      --color-text-tertiary: #666666;
      --color-success: #10b981;
      --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.5);
      --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.3);
      --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.4);
      --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.5);
      --radius-sm: 8px;
      --radius-md: 12px;
      --radius-lg: 16px;
      --radius-xl: 20px;
      --radius-full: 9999px;
      --transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
    }

    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }

    body {
      font-family: -apple-system, BlinkMacSystemFont, 'SF Pro Display', 'Segoe UI', system-ui, sans-serif;
      background: var(--color-background);
      color: var(--color-text-primary);
      line-height: 1.6;
      -webkit-font-smoothing: antialiased;
      overflow-x: hidden;
    }

    #app {
      max-width: 900px;
      margin: 0 auto;
      padding: clamp(1.5rem, 3vw, 2.5rem);
      min-height: 100vh;
      display: flex;
      flex-direction: column;
      gap: 1rem;
    }

    /* Header Section */
    .top-row {
      display: flex;
      gap: 0.75rem;
      align-items: flex-end;
    }

    .file-label {
      position: relative;
      overflow: hidden;
      background: var(--color-primary);
      color: #000000;
      padding: 0.75rem 1.25rem;
      border-radius: var(--radius-full);
      font-weight: 600;
      font-size: 0.875rem;
      cursor: pointer;
      transition: var(--transition);
      box-shadow: var(--shadow-sm);
      border: none;
      display: inline-flex;
      align-items: center;
      gap: 0.5rem;
      white-space: nowrap;
    }

    .file-label::before {
      content: '📁';
      font-size: 1rem;
    }

    .file-label:hover {
      background: var(--color-primary-hover);
      transform: translateY(-1px);
      box-shadow: var(--shadow-md);
    }

    .file-label:active {
      transform: translateY(0);
    }

    .file-label input {
      position: absolute;
      opacity: 0;
      pointer-events: none;
    }

    .control {
      flex: 1;
      display: flex;
      flex-direction: column;
      gap: 0.5rem;
    }

    .control > label {
      font-size: 0.6875rem;
      font-weight: 600;
      text-transform: uppercase;
      letter-spacing: 0.05em;
      color: var(--color-text-tertiary);
    }

    .block-size-input-row {
      display: flex;
      align-items: center;
      gap: 0.5rem;
      background: var(--color-surface);
      border: 1px solid var(--color-stroke);
      border-radius: var(--radius-full);
      padding: 0.25rem;
    }

    .block-size-input-row button {
      width: 36px;
      height: 36px;
      border-radius: 50%;
      border: none;
      background: var(--color-surface-elevated);
      color: var(--color-text-primary);
      font-size: 1.125rem;
      font-weight: 600;
      cursor: pointer;
      transition: var(--transition);
      display: flex;
      align-items: center;
      justify-content: center;
    }

    .block-size-input-row button:hover {
      background: var(--color-surface-hover);
      transform: scale(1.05);
    }

    .block-size-input-row button:active {
      transform: scale(0.95);
    }

    .block-size-input-row input {
      flex: 1;
      background: transparent;
      border: none;
      color: var(--color-text-primary);
      text-align: center;
      font-size: 0.9375rem;
      font-weight: 600;
      padding: 0 0.5rem;
      min-width: 60px;
      -moz-appearance: textfield;
    }

    .block-size-input-row input::-webkit-inner-spin-button,
    .block-size-input-row input::-webkit-outer-spin-button {
      -webkit-appearance: none;
    }

    .block-size-input-row input:focus {
      outline: none;
    }

    .value-row {
      display: flex;
      justify-content: flex-end;
      font-size: 0.75rem;
      color: var(--color-text-secondary);
      font-variant-numeric: tabular-nums;
    }

    /* Tabs */
    .tabs-header {
      display: inline-flex;
      gap: 0.25rem;
      padding: 0.25rem;
      background: var(--color-surface);
      border: 1px solid var(--color-stroke);
      border-radius: var(--radius-full);
      width: fit-content;
    }

    .tab-button {
      padding: 0.625rem 1.25rem;
      background: transparent;
      border: none;
      border-radius: var(--radius-full);
      color: var(--color-text-secondary);
      font-size: 0.875rem;
      font-weight: 600;
      cursor: pointer;
      transition: var(--transition);
      position: relative;
    }

    .tab-button.active {
      background: var(--color-primary);
      color: #000000;
      box-shadow: var(--shadow-sm);
    }

    .tab-button:not(.active):hover {
      color: var(--color-text-primary);
      background: var(--color-surface-elevated);
    }

    /* Tab Content */
    .tabs-body {
      flex: 1;
      display: flex;
      min-height: 0;
    }

    .tab-panel {
      display: none;
      flex: 1;
      flex-direction: column;
      gap: 1rem;
    }

    .tab-panel.active {
      display: flex;
    }

    /* Canvas Area */
    .canvas-wrap {
      position: relative;
      flex: 1;
      min-height: 350px;
      border-radius: var(--radius-lg);
      background: var(--color-surface);
      border: 1px solid var(--color-stroke);
      overflow: hidden;
      display: flex;
      align-items: center;
      justify-content: center;
      transition: var(--transition);
    }

    .canvas-wrap.dragover {
      border-color: var(--color-accent);
      background: rgba(59, 130, 246, 0.05);
    }

    #previewCanvas {
      max-width: 100%;
      max-height: 100%;
      display: none;
      image-rendering: pixelated;
      border-radius: var(--radius-md);
    }

    #placeholder {
      text-align: center;
      color: var(--color-text-tertiary);
      font-size: 0.9375rem;
      padding: 2rem;
    }

    /* Action Buttons */
    .bottom-row {
      display: grid;
      grid-template-columns: repeat(3, 1fr);
      gap: 0.75rem;
    }

    .bottom-row button {
      padding: 0.875rem 1rem;
      border-radius: var(--radius-md);
      font-size: 0.875rem;
      font-weight: 600;
      cursor: pointer;
      transition: var(--transition);
      border: 1px solid var(--color-stroke);
      background: var(--color-surface);
      color: var(--color-text-primary);
    }

    .bottom-row button:first-child {
      background: var(--color-primary);
      color: #000000;
      border-color: transparent;
    }

    .bottom-row button:first-child:hover:not(:disabled) {
      background: var(--color-primary-hover);
      transform: translateY(-2px);
      box-shadow: var(--shadow-md);
    }

    .bottom-row button:not(:first-child):hover:not(:disabled) {
      background: var(--color-surface-elevated);
      border-color: var(--color-stroke);
      transform: translateY(-2px);
    }

    .bottom-row button:active:not(:disabled) {
      transform: translateY(0);
    }

    .bottom-row button:disabled {
      opacity: 0.4;
      cursor: not-allowed;
      transform: none;
    }

    /* Grid Preview */
    .grid-preview {
      border-radius: var(--radius-lg);
      background: var(--color-surface);
      border: 1px solid var(--color-stroke);
      padding: 1rem;
      display: flex;
      align-items: center;
      justify-content: center;
      min-height: 100px;
      max-height: 140px;
    }

    #gridPreviewCanvas {
      max-width: 100%;
      max-height: 100%;
      image-rendering: pixelated;
      border-radius: var(--radius-sm);
    }

    /* Code Panel */
    .code-panel {
      flex: 1;
      display: flex;
      flex-direction: column;
      gap: 1rem;
      background: var(--color-surface);
      border: 1px solid var(--color-stroke);
      border-radius: var(--radius-xl);
      padding: 1.5rem;
    }

    .code-header {
      display: flex;
      justify-content: space-between;
      align-items: center;
      gap: 1rem;
    }

    .code-header > span {
      font-size: 0.6875rem;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.05em;
      color: var(--color-text-tertiary);
    }

    .code-header-right {
      display: flex;
      align-items: center;
      gap: 1rem;
    }

    #statsLabel {
      font-size: 0.75rem;
      color: var(--color-text-secondary);
      font-variant-numeric: tabular-nums;
    }

    #copyCode {
      padding: 0.5rem 1rem;
      background: var(--color-primary);
      color: #000000;
      border: none;
      border-radius: var(--radius-full);
      font-size: 0.8125rem;
      font-weight: 600;
      cursor: pointer;
      transition: var(--transition);
    }

    #copyCode:hover:not(:disabled) {
      background: var(--color-primary-hover);
      transform: translateY(-1px);
    }

    #copyCode:disabled {
      opacity: 0.4;
      cursor: not-allowed;
      transform: none;
    }

    .code-output {
      flex: 1;
      min-height: 300px;
      padding: 1rem;
      background: #000000;
      border: 1px solid var(--color-stroke-subtle);
      border-radius: var(--radius-md);
      color: var(--color-text-primary);
      font-family: 'SF Mono', Monaco, 'Cascadia Code', 'Courier New', monospace;
      font-size: 0.8125rem;
      line-height: 1.6;
      overflow: auto;
      word-break: break-all;
    }

    /* Responsive */
    @media (max-width: 768px) {
      .top-row {
        flex-direction: column;
        align-items: stretch;
      }

      .control {
        width: 100%;
      }

      .tabs-header {
        width: 100%;
      }

      .tab-button {
        flex: 1;
      }

      .bottom-row {
        grid-template-columns: 1fr;
      }

      .canvas-wrap {
        min-height: 300px;
      }

      .code-output {
        min-height: 200px;
      }
    }

    /* Animations */
    @keyframes fadeIn {
      from { opacity: 0; transform: translateY(10px); }
      to { opacity: 1; transform: translateY(0); }
    }

    .tab-panel.active {
      animation: fadeIn 0.3s ease;
    }

    /* Focus styles */
    button:focus-visible,
    input:focus-visible {
      outline: 2px solid var(--color-accent);
      outline-offset: 2px;
    }

    /* Footer */
    .footer {
      text-align: center;
      padding: 1.5rem 0 0.5rem;
      font-size: 0.8125rem;
      color: var(--color-text-tertiary);
      border-top: 1px solid var(--color-stroke-subtle);
      margin-top: auto;
    }

    .footer a {
      color: var(--color-text-secondary);
      text-decoration: none;
      transition: var(--transition);
      font-weight: 600;
    }

    .footer a:hover {
      color: var(--color-text-primary);
    }

    .heart {
      color: #ef4444;
      display: inline-block;
      animation: heartbeat 1.5s ease-in-out infinite;
    }

    @keyframes heartbeat {
      0%, 100% { transform: scale(1); }
      10%, 30% { transform: scale(1.1); }
      20% { transform: scale(0.95); }
    }