:root {
    --primary-color: #667eea;
    --primary-dark: #5568d3;
    --secondary-color: #764ba2;
    --success-color: #10b981;
    --success-dark: #059669;
    --warning-color: #f59e0b;
    --danger-color: #ef4444;
    --gray-50: #f9fafb;
    --gray-100: #f3f4f6;
    --gray-200: #e5e7eb;
    --gray-300: #d1d5db;
    --gray-400: #9ca3af;
    --gray-500: #6b7280;
    --gray-600: #4b5563;
    --gray-700: #374151;
    --gray-800: #1f2937;
    --gray-900: #111827;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    --radius-sm: 6px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-xl: 16px;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen', 'Ubuntu', 'Cantarell', sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    padding: 20px;
    color: var(--gray-800);
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    background: white;
    border-radius: var(--radius-xl);
    padding: 40px;
    box-shadow: var(--shadow-xl);
    animation: fadeIn 0.5s ease-out;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.header {
    text-align: center;
    margin-bottom: 30px;
}

.logo {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 12px;
    margin-bottom: 12px;
}

.logo-icon {
    width: 40px;
    height: 40px;
}

h1 {
    color: var(--gray-900);
    font-size: 2.2em;
    font-weight: 700;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.subtitle {
    color: var(--gray-500);
    font-size: 1.05em;
}

.toolbar {
    display: flex;
    flex-wrap: wrap;
    gap: 20px;
    align-items: center;
    margin-bottom: 24px;
    padding: 20px;
    background: var(--gray-50);
    border-radius: var(--radius-lg);
    border: 1px solid var(--gray-200);
}

.toolbar-section {
    display: flex;
    gap: 12px;
    flex-wrap: wrap;
}

.divider {
    width: 1px;
    height: 40px;
    background: var(--gray-300);
}

.upload-input-hidden {
    display: none;
}

.btn {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 10px 20px;
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    font-size: 14px;
    font-weight: 500;
    transition: all 0.2s ease;
    box-shadow: var(--shadow-sm);
}

.btn:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.btn:active:not(:disabled) {
    transform: translateY(0);
}

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

.btn-icon {
    width: 18px;
    height: 18px;
}

.btn-primary {
    background: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
    color: white;
}

.btn-primary:hover:not(:disabled) {
    background: linear-gradient(135deg, var(--primary-dark), #4755c3);
}

.btn-secondary {
    background: white;
    color: var(--gray-700);
    border: 1px solid var(--gray-300);
}

.btn-secondary:hover:not(:disabled) {
    background: var(--gray-50);
    border-color: var(--gray-400);
}

.btn-success {
    background: linear-gradient(135deg, var(--success-color), var(--success-dark));
    color: white;
}

.btn-success:hover:not(:disabled) {
    background: linear-gradient(135deg, var(--success-dark), #047857);
}

.settings {
    display: flex;
    gap: 24px;
    flex-wrap: wrap;
    margin-left: auto;
}

.setting-item {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.setting-header {
    display: flex;
    align-items: center;
    gap: 6px;
    font-size: 13px;
    color: var(--gray-600);
    font-weight: 500;
}

.setting-icon {
    width: 16px;
    height: 16px;
    color: var(--primary-color);
}

.slider-container {
    display: flex;
    align-items: center;
    gap: 12px;
}

input[type="range"] {
    -webkit-appearance: none;
    appearance: none;
    width: 120px;
    height: 6px;
    background: var(--gray-200);
    border-radius: 3px;
    outline: none;
    cursor: pointer;
}

input[type="range"]::-webkit-slider-thumb {
    -webkit-appearance: none;
    appearance: none;
    width: 18px;
    height: 18px;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    border-radius: 50%;
    cursor: pointer;
    box-shadow: var(--shadow-md);
    transition: transform 0.2s;
}

input[type="range"]::-webkit-slider-thumb:hover {
    transform: scale(1.1);
}

input[type="range"]::-moz-range-thumb {
    width: 18px;
    height: 18px;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    border-radius: 50%;
    cursor: pointer;
    border: none;
    box-shadow: var(--shadow-md);
}

.slider-value {
    min-width: 40px;
    padding: 4px 8px;
    background: white;
    border: 1px solid var(--gray-300);
    border-radius: var(--radius-sm);
    font-size: 13px;
    font-weight: 600;
    color: var(--gray-700);
    text-align: center;
}

.canvas-container {
    position: relative;
    min-height: 450px;
    background: var(--gray-50);
    border: 2px dashed var(--gray-300);
    border-radius: var(--radius-lg);
    display: flex;
    align-items: center;
    justify-content: center;
    overflow: hidden;
    transition: all 0.3s ease;
}

.canvas-container.drag-over {
    border-color: var(--primary-color);
    background: linear-gradient(135deg, rgba(102, 126, 234, 0.05), rgba(118, 75, 162, 0.05));
}

#canvas {
    display: none;
    max-width: 100%;
    cursor: crosshair;
    border-radius: var(--radius-sm);
}

#canvas.active {
    display: block;
}

.placeholder {
    text-align: center;
    padding: 60px 40px;
    transition: all 0.3s ease;
}

.placeholder-icon {
    width: 80px;
    height: 80px;
    color: var(--gray-400);
    margin: 0 auto 20px;
}

.placeholder-text {
    font-size: 1.3em;
    font-weight: 600;
    color: var(--gray-600);
    margin-bottom: 8px;
}

.placeholder-subtext {
    font-size: 1em;
    color: var(--gray-500);
    margin-bottom: 12px;
}

.placeholder-hint {
    font-size: 0.9em;
    color: var(--gray-400);
    padding: 8px 16px;
    background: var(--gray-100);
    border-radius: var(--radius-md);
    display: inline-block;
}

.brush-preview {
    position: absolute;
    pointer-events: none;
    border: 2px solid var(--primary-color);
    border-radius: 50%;
    display: none;
    box-shadow: 0 0 0 1px rgba(102, 126, 234, 0.3);
    z-index: 10;
}

.status-bar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 12px 16px;
    margin-top: 16px;
    background: var(--gray-50);
    border-radius: var(--radius-md);
    border: 1px solid var(--gray-200);
    font-size: 13px;
}

.status-text {
    color: var(--gray-600);
    font-weight: 500;
}

.image-info {
    color: var(--gray-500);
}

.tips {
    margin-top: 30px;
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 16px;
}

.tip-item {
    display: flex;
    gap: 12px;
    padding: 16px;
    background: var(--gray-50);
    border-radius: var(--radius-md);
    border: 1px solid var(--gray-200);
    transition: all 0.2s ease;
}

.tip-item:hover {
    background: white;
    box-shadow: var(--shadow-md);
    border-color: var(--primary-color);
}

.tip-icon {
    width: 24px;
    height: 24px;
    color: var(--primary-color);
    flex-shrink: 0;
}

.tip-content h4 {
    font-size: 14px;
    font-weight: 600;
    color: var(--gray-800);
    margin-bottom: 4px;
}

.tip-content p {
    font-size: 13px;
    color: var(--gray-600);
    line-height: 1.5;
}

@media (max-width: 768px) {
    body {
        padding: 10px;
    }

    .container {
        padding: 20px;
    }

    h1 {
        font-size: 1.6em;
    }

    .toolbar {
        flex-direction: column;
        align-items: stretch;
    }

    .toolbar-section {
        justify-content: center;
    }

    .divider {
        display: none;
    }

    .settings {
        margin-left: 0;
        flex-direction: column;
    }

    input[type="range"] {
        width: 100%;
    }

    .tips {
        grid-template-columns: 1fr;
    }

    .status-bar {
        flex-direction: column;
        gap: 8px;
        text-align: center;
    }
}

@media (max-width: 480px) {
    .btn {
        width: 100%;
        justify-content: center;
    }

    .placeholder {
        padding: 40px 20px;
    }

    .placeholder-icon {
        width: 60px;
        height: 60px;
    }
}