/* CSS Variables */
:root {
    --primary-color: #6366f1;
    --primary-hover: #4f46e5;
    --primary-light: #e0e7ff;
    --secondary-color: #10b981;
    --secondary-hover: #059669;
    --danger-color: #ef4444;
    --danger-hover: #dc2626;
    --background: #f8fafc;
    --surface: #ffffff;
    --surface-hover: #f1f5f9;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --text-muted: #94a3b8;
    --border-color: #e2e8f0;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -2px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -4px rgba(0, 0, 0, 0.1);
    --radius-sm: 6px;
    --radius-md: 10px;
    --radius-lg: 16px;
    --transition: all 0.2s ease;
}

/* Reset & Base */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background: var(--background);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
}

/* App Container */
.app-container {
    max-width: 900px;
    margin: 0 auto;
    padding: 20px;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* Header */
header {
    text-align: center;
    margin-bottom: 30px;
    padding: 20px 0;
}

header h1 {
    font-size: 2.25rem;
    font-weight: 700;
    color: var(--primary-color);
    margin-bottom: 8px;
}

header .subtitle {
    font-size: 1.1rem;
    color: var(--text-secondary);
}

/* Main Content */
main {
    flex: 1;
}

/* Selection Panel */
.selection-panel {
    background: var(--surface);
    border-radius: var(--radius-lg);
    padding: 24px;
    box-shadow: var(--shadow-md);
    margin-bottom: 24px;
}

.selection-group {
    margin-bottom: 24px;
}

.selection-group:last-of-type {
    margin-bottom: 20px;
}

.selection-group h3 {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 12px;
    padding-bottom: 8px;
    border-bottom: 2px solid var(--primary-light);
}

/* Checkbox Grid */
.checkbox-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
    gap: 10px;
}

.checkbox-item {
    display: flex;
    align-items: center;
    padding: 10px 12px;
    background: var(--surface-hover);
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: var(--transition);
    border: 2px solid transparent;
}

.checkbox-item:hover {
    background: var(--primary-light);
}

.checkbox-item input[type="checkbox"] {
    display: none;
}

.checkbox-item .checkmark {
    width: 20px;
    height: 20px;
    border: 2px solid var(--border-color);
    border-radius: 4px;
    margin-right: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
    flex-shrink: 0;
}

.checkbox-item input[type="checkbox"]:checked + .checkmark {
    background: var(--primary-color);
    border-color: var(--primary-color);
}

.checkbox-item input[type="checkbox"]:checked + .checkmark::after {
    content: '✓';
    color: white;
    font-size: 12px;
    font-weight: bold;
}

.checkbox-item .label-text {
    font-size: 0.9rem;
    color: var(--text-primary);
}

/* Quick Select Buttons */
.quick-select {
    display: flex;
    gap: 10px;
    margin-top: 10px;
}

.btn-small {
    padding: 6px 12px;
    font-size: 0.8rem;
    background: var(--surface-hover);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: var(--transition);
    color: var(--text-secondary);
}

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

/* Settings Grid */
.settings-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
    gap: 16px;
}

.setting-item {
    display: flex;
    flex-direction: column;
    gap: 6px;
}

.setting-item label {
    font-size: 0.85rem;
    font-weight: 500;
    color: var(--text-secondary);
}

.setting-item input[type="number"] {
    padding: 10px 12px;
    border: 2px solid var(--border-color);
    border-radius: var(--radius-sm);
    font-size: 1rem;
    transition: var(--transition);
    width: 100%;
}

.setting-item input[type="number"]:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px var(--primary-light);
}

/* Generate Button */
.btn-generate {
    width: 100%;
    padding: 16px 24px;
    font-size: 1.1rem;
    font-weight: 600;
    color: white;
    background: linear-gradient(135deg, var(--primary-color), var(--primary-hover));
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 10px;
    box-shadow: var(--shadow-md);
}

.btn-generate:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn-generate:active {
    transform: translateY(0);
}

.btn-icon {
    font-size: 1.2rem;
}

/* Workout Section */
.workout-section {
    background: var(--surface);
    border-radius: var(--radius-lg);
    padding: 24px;
    box-shadow: var(--shadow-md);
    margin-bottom: 24px;
    display: none;
}

.workout-section.active {
    display: block;
    animation: fadeIn 0.3s ease;
}

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

.workout-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
    flex-wrap: wrap;
    gap: 12px;
}

.workout-header h2 {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
}

.btn-secondary {
    padding: 10px 16px;
    font-size: 0.9rem;
    font-weight: 500;
    color: var(--primary-color);
    background: var(--primary-light);
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    gap: 6px;
}

.btn-secondary:hover {
    background: var(--primary-color);
    color: white;
}

/* Workout List */
.workout-list {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.exercise-card {
    background: var(--surface-hover);
    border-radius: var(--radius-md);
    padding: 16px 20px;
    display: flex;
    align-items: center;
    gap: 16px;
    transition: var(--transition);
    border-left: 4px solid var(--primary-color);
}

.exercise-card:hover {
    transform: translateX(4px);
    box-shadow: var(--shadow-sm);
}

.exercise-number {
    width: 36px;
    height: 36px;
    background: var(--primary-color);
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    font-size: 1rem;
    flex-shrink: 0;
}

.exercise-details {
    flex: 1;
    min-width: 0;
}

.exercise-name {
    font-size: 1.05rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 4px;
}

.exercise-meta {
    display: flex;
    gap: 16px;
    flex-wrap: wrap;
}

.exercise-meta span {
    font-size: 0.85rem;
    color: var(--text-secondary);
    display: flex;
    align-items: center;
    gap: 4px;
}

.exercise-tags {
    display: flex;
    gap: 8px;
    flex-wrap: wrap;
}

.tag {
    padding: 4px 10px;
    font-size: 0.75rem;
    font-weight: 500;
    border-radius: 20px;
    text-transform: capitalize;
}

.tag-muscle {
    background: #dbeafe;
    color: #1e40af;
}

.tag-equipment {
    background: #dcfce7;
    color: #166534;
}

/* Workout Summary */
.workout-summary {
    margin-top: 20px;
    padding: 16px;
    background: linear-gradient(135deg, var(--primary-light), #c7d2fe);
    border-radius: var(--radius-md);
}

.summary-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: 16px;
    text-align: center;
}

.summary-item {
    padding: 8px;
}

.summary-value {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary-hover);
}

.summary-label {
    font-size: 0.85rem;
    color: var(--text-secondary);
}

/* Timer Section */
.timer-section {
    background: var(--surface);
    border-radius: var(--radius-lg);
    padding: 24px;
    box-shadow: var(--shadow-md);
    text-align: center;
    display: none;
}

.timer-section.active {
    display: block;
    animation: fadeIn 0.3s ease;
}

.timer-section h2 {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 20px;
}

.timer-display {
    margin-bottom: 24px;
}

.timer-value {
    font-size: 4rem;
    font-weight: 700;
    color: var(--primary-color);
    font-family: 'SF Mono', 'Fira Code', monospace;
    line-height: 1;
    margin-bottom: 8px;
}

.timer-label {
    font-size: 1rem;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 1px;
}

.timer-value.warning {
    color: #f59e0b;
}

.timer-value.danger {
    color: var(--danger-color);
    animation: pulse 0.5s ease infinite;
}

@keyframes pulse {
    0%, 100% { opacity: 1; }
    50% { opacity: 0.6; }
}

.timer-controls {
    display: flex;
    justify-content: center;
    gap: 12px;
    flex-wrap: wrap;
    margin-bottom: 20px;
}

.btn-timer {
    padding: 12px 20px;
    font-size: 0.95rem;
    font-weight: 500;
    color: white;
    background: var(--secondary-color);
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    gap: 8px;
}

.btn-timer:hover {
    background: var(--secondary-hover);
    transform: translateY(-1px);
}

.btn-timer.btn-stop {
    background: var(--danger-color);
}

.btn-timer.btn-stop:hover {
    background: var(--danger-hover);
}

.timer-presets {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 10px;
    flex-wrap: wrap;
    padding-top: 16px;
    border-top: 1px solid var(--border-color);
}

.timer-presets span {
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.btn-preset {
    padding: 8px 14px;
    font-size: 0.85rem;
    font-weight: 500;
    color: var(--text-primary);
    background: var(--surface-hover);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: var(--transition);
}

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

/* Footer */
footer {
    text-align: center;
    padding: 24px 0;
    margin-top: 40px;
    border-top: 1px solid var(--border-color);
}

footer p {
    font-size: 0.9rem;
    color: var(--text-secondary);
}

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

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

/* Responsive Design */
@media (max-width: 768px) {
    .app-container {
        padding: 16px;
    }

    header h1 {
        font-size: 1.75rem;
    }

    header .subtitle {
        font-size: 1rem;
    }

    .selection-panel {
        padding: 16px;
    }

    .checkbox-grid {
        grid-template-columns: repeat(2, 1fr);
    }

    .settings-grid {
        grid-template-columns: repeat(2, 1fr);
    }

    .workout-header {
        flex-direction: column;
        align-items: flex-start;
    }

    .exercise-card {
        flex-wrap: wrap;
    }

    .exercise-tags {
        width: 100%;
        margin-top: 8px;
    }

    .timer-value {
        font-size: 3rem;
    }

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

    .btn-timer {
        justify-content: center;
    }

    .summary-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 480px) {
    header h1 {
        font-size: 1.5rem;
    }

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

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

    .exercise-card {
        padding: 12px;
    }

    .exercise-meta {
        flex-direction: column;
        gap: 4px;
    }

    .timer-value {
        font-size: 2.5rem;
    }

    .timer-presets {
        flex-direction: column;
    }
}

/* Accessibility */
@media (prefers-reduced-motion: reduce) {
    * {
        animation: none !important;
        transition: none !important;
    }
}

/* Focus states for accessibility */
button:focus-visible,
input:focus-visible,
a:focus-visible {
    outline: 2px solid var(--primary-color);
    outline-offset: 2px;
}