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

:root {
    --primary-color: #3b82f6;
    --primary-hover: #2563eb;
    --bg-color: #f8fafc;
    --toolbar-bg: #ffffff;
    --text-color: #1e293b;
    --text-muted: #64748b;
    --border-color: #e2e8f0;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --radius: 8px;
}

html, body {
    height: 100%;
    overflow: hidden;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
}

.app-container {
    display: flex;
    flex-direction: column;
    height: 100vh;
}

/* Toolbar */
.toolbar {
    display: flex;
    align-items: center;
    gap: 16px;
    padding: 12px 20px;
    background: var(--toolbar-bg);
    border-bottom: 1px solid var(--border-color);
    box-shadow: var(--shadow);
    flex-wrap: wrap;
    z-index: 100;
}

.toolbar-section {
    display: flex;
    align-items: center;
    gap: 8px;
}

.app-title {
    font-size: 1.25rem;
    font-weight: 600;
    color: var(--text-color);
}

/* Tool Buttons */
.tool-btn {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 44px;
    height: 44px;
    border: 2px solid var(--border-color);
    border-radius: var(--radius);
    background: var(--toolbar-bg);
    color: var(--text-muted);
    cursor: pointer;
    transition: all 0.2s ease;
}

.tool-btn:hover {
    border-color: var(--primary-color);
    color: var(--primary-color);
}

.tool-btn.active {
    border-color: var(--primary-color);
    background: var(--primary-color);
    color: white;
}

/* Color Picker */
.color-picker-wrapper {
    position: relative;
    cursor: pointer;
}

.color-picker-wrapper input[type="color"] {
    position: absolute;
    opacity: 0;
    width: 44px;
    height: 44px;
    cursor: pointer;
}

.color-preview {
    display: block;
    width: 44px;
    height: 44px;
    border-radius: var(--radius);
    border: 2px solid var(--border-color);
    background: #000000;
    transition: transform 0.2s ease;
}

.color-picker-wrapper:hover .color-preview {
    transform: scale(1.05);
}

/* Brush Size */
.brush-size-section {
    gap: 12px;
}

.brush-label {
    font-size: 0.875rem;
    color: var(--text-muted);
    font-weight: 500;
}

#brush-size {
    width: 100px;
    height: 6px;
    -webkit-appearance: none;
    appearance: none;
    background: var(--border-color);
    border-radius: 3px;
    cursor: pointer;
}

#brush-size::-webkit-slider-thumb {
    -webkit-appearance: none;
    width: 18px;
    height: 18px;
    background: var(--primary-color);
    border-radius: 50%;
    cursor: pointer;
    transition: transform 0.2s ease;
}

#brush-size::-webkit-slider-thumb:hover {
    transform: scale(1.2);
}

#brush-size::-moz-range-thumb {
    width: 18px;
    height: 18px;
    background: var(--primary-color);
    border-radius: 50%;
    border: none;
    cursor: pointer;
}

#brush-size-value {
    font-size: 0.875rem;
    color: var(--text-muted);
    min-width: 35px;
}

/* Action Buttons */
.actions {
    margin-left: auto;
}

.action-btn {
    display: flex;
    align-items: center;
    gap: 6px;
    padding: 10px 16px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    background: var(--toolbar-bg);
    color: var(--text-color);
    font-size: 0.875rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s ease;
}

.action-btn:hover {
    background: var(--bg-color);
    border-color: var(--text-muted);
}

.action-btn.primary {
    background: var(--primary-color);
    border-color: var(--primary-color);
    color: white;
}

.action-btn.primary:hover {
    background: var(--primary-hover);
    border-color: var(--primary-hover);
}

/* Canvas Container */
.canvas-container {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 20px;
    overflow: hidden;
    background: var(--bg-color);
}

#whiteboard {
    background: white;
    border-radius: var(--radius);
    box-shadow: var(--shadow-lg);
    cursor: crosshair;
    touch-action: none;
}

/* Footer */
.footer {
    padding: 12px 20px;
    text-align: center;
    background: var(--toolbar-bg);
    border-top: 1px solid var(--border-color);
}

.footer p {
    font-size: 0.875rem;
    color: var(--text-muted);
}

.footer a {
    color: var(--primary-color);
    text-decoration: none;
    font-weight: 500;
    transition: color 0.2s ease;
}

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

/* Mobile Responsive */
@media (max-width: 768px) {
    .toolbar {
        padding: 10px 12px;
        gap: 10px;
        justify-content: center;
    }

    .app-title {
        font-size: 1rem;
    }

    .tool-btn {
        width: 40px;
        height: 40px;
    }

    .color-preview,
    .color-picker-wrapper input[type="color"] {
        width: 40px;
        height: 40px;
    }

    .brush-size-section {
        order: 5;
        width: 100%;
        justify-content: center;
    }

    #brush-size {
        width: 150px;
    }

    .actions {
        margin-left: 0;
    }

    .btn-text {
        display: none;
    }

    .action-btn {
        padding: 10px 12px;
    }

    .canvas-container {
        padding: 10px;
    }

    .footer {
        padding: 10px 12px;
    }

    .footer p {
        font-size: 0.75rem;
    }
}

@media (max-width: 480px) {
    .toolbar {
        padding: 8px;
        gap: 6px;
    }

    .toolbar-section {
        gap: 4px;
    }

    .tool-btn {
        width: 36px;
        height: 36px;
    }

    .tool-btn svg {
        width: 20px;
        height: 20px;
    }

    .color-preview,
    .color-picker-wrapper input[type="color"] {
        width: 36px;
        height: 36px;
    }

    .action-btn {
        padding: 8px 10px;
    }

    .action-btn svg {
        width: 18px;
        height: 18px;
    }
}

/* Touch device optimizations */
@media (hover: none) {
    .tool-btn:hover {
        border-color: var(--border-color);
        color: var(--text-muted);
    }

    .tool-btn.active:hover {
        border-color: var(--primary-color);
        color: white;
    }

    .color-picker-wrapper:hover .color-preview {
        transform: none;
    }

    #brush-size::-webkit-slider-thumb:hover {
        transform: none;
    }
}