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

:root {
    --primary-color: #4f46e5;
    --secondary-color: #7c3aed;
    --success-color: #10b981;
    --warning-color: #f59e0b;
    --danger-color: #ef4444;
    --bg-primary: #ffffff;
    --bg-secondary: #f9fafb;
    --bg-tertiary: #f3f4f6;
    --text-primary: #111827;
    --text-secondary: #6b7280;
    --border-color: #e5e7eb;
    --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);
    --transition: all 0.3s ease;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background-color: var(--bg-secondary);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1rem;
}

/* Header */
header {
    background-color: var(--bg-primary);
    padding: 2rem 0;
    text-align: center;
    box-shadow: var(--shadow-sm);
    margin-bottom: 2rem;
}

h1 {
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

.subtitle {
    font-size: 1.25rem;
    color: var(--text-secondary);
    margin-bottom: 1.5rem;
}

/* Language Selector */
.language-selector {
    display: inline-flex;
    gap: 0.5rem;
    background-color: var(--bg-tertiary);
    padding: 0.25rem;
    border-radius: 0.5rem;
}

.lang-btn {
    padding: 0.5rem 1rem;
    border: none;
    background: transparent;
    color: var(--text-secondary);
    font-size: 0.875rem;
    font-weight: 500;
    border-radius: 0.375rem;
    cursor: pointer;
    transition: var(--transition);
}

.lang-btn:hover {
    background-color: rgba(79, 70, 229, 0.1);
    color: var(--primary-color);
}

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

/* Exercise Grid */
.exercise-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 1.5rem;
    margin-bottom: 3rem;
}

.exercise-card {
    background-color: var(--bg-primary);
    border-radius: 1rem;
    padding: 2rem;
    box-shadow: var(--shadow-md);
    cursor: pointer;
    transition: var(--transition);
    border: 2px solid transparent;
    position: relative;
    overflow: hidden;
}

.exercise-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 4px;
    background: linear-gradient(90deg, var(--primary-color), var(--secondary-color));
    transform: translateX(-100%);
    transition: transform 0.3s ease;
}

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

.exercise-card:hover::before {
    transform: translateX(0);
}

.exercise-card.selected {
    border-color: var(--primary-color);
    background-color: rgba(79, 70, 229, 0.05);
}

.exercise-card.active {
    border-color: var(--success-color);
    background-color: rgba(16, 185, 129, 0.05);
}

.exercise-icon {
    font-size: 3rem;
    margin-bottom: 1rem;
    display: inline-block;
    animation: bounce 2s infinite;
}

@keyframes bounce {
    0%, 100% { transform: translateY(0); }
    50% { transform: translateY(-10px); }
}

.exercise-card h3 {
    font-size: 1.25rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
    color: var(--text-primary);
}

.exercise-card p {
    color: var(--text-secondary);
    font-size: 0.875rem;
    margin-bottom: 1rem;
}

.duration {
    display: inline-block;
    background-color: var(--bg-tertiary);
    padding: 0.25rem 0.75rem;
    border-radius: 2rem;
    font-size: 0.75rem;
    font-weight: 500;
    color: var(--primary-color);
}

/* Timer Section */
.timer-section {
    background-color: var(--bg-primary);
    border-radius: 1rem;
    padding: 2.5rem;
    box-shadow: var(--shadow-md);
    margin-bottom: 2rem;
}

.timer-section h2 {
    font-size: 1.75rem;
    font-weight: 600;
    margin-bottom: 2rem;
    text-align: center;
    color: var(--text-primary);
}

.timer-display {
    text-align: center;
    margin-bottom: 2rem;
}

.time-display {
    font-size: 4rem;
    font-weight: 700;
    color: var(--primary-color);
    font-variant-numeric: tabular-nums;
    letter-spacing: 0.05em;
}

.current-exercise {
    font-size: 1.25rem;
    color: var(--text-secondary);
    margin-top: 0.5rem;
    min-height: 2rem;
}

.timer-controls {
    display: flex;
    justify-content: center;
    gap: 1rem;
    margin-bottom: 2rem;
}

.btn {
    padding: 0.75rem 2rem;
    border: none;
    border-radius: 0.5rem;
    font-size: 1rem;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition);
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
}

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

.btn-primary:hover {
    background-color: #4338ca;
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.btn-secondary {
    background-color: var(--bg-tertiary);
    color: var(--text-primary);
}

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

/* Progress Bar */
.progress-bar {
    width: 100%;
    height: 0.5rem;
    background-color: var(--bg-tertiary);
    border-radius: 0.25rem;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--primary-color), var(--secondary-color));
    width: 0%;
    transition: width 1s linear;
}

/* Reminder Section */
.reminder-section {
    background-color: var(--bg-primary);
    border-radius: 1rem;
    padding: 2rem;
    box-shadow: var(--shadow-md);
    margin-bottom: 2rem;
}

.reminder-section h2 {
    font-size: 1.5rem;
    font-weight: 600;
    margin-bottom: 1.5rem;
    color: var(--text-primary);
}

.reminder-options {
    display: flex;
    flex-wrap: wrap;
    gap: 1.5rem;
    margin-bottom: 1rem;
}

.reminder-option {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    cursor: pointer;
    user-select: none;
}

.reminder-option input[type="checkbox"] {
    width: 1.25rem;
    height: 1.25rem;
    cursor: pointer;
    accent-color: var(--primary-color);
}

.reminder-option span {
    font-size: 1rem;
    color: var(--text-primary);
}

.notification-status {
    font-size: 0.875rem;
    color: var(--success-color);
    opacity: 0;
    transition: opacity 0.3s ease;
    margin-top: 1rem;
}

.notification-status.show {
    opacity: 1;
}

/* Footer */
footer {
    text-align: center;
    padding: 2rem 0;
    color: var(--text-secondary);
    font-size: 0.875rem;
}

/* Responsive Design */
@media (max-width: 768px) {
    h1 {
        font-size: 2rem;
    }
    
    .subtitle {
        font-size: 1rem;
    }
    
    .exercise-grid {
        grid-template-columns: 1fr;
        gap: 1rem;
    }
    
    .exercise-card {
        padding: 1.5rem;
    }
    
    .time-display {
        font-size: 3rem;
    }
    
    .timer-controls {
        flex-wrap: wrap;
    }
    
    .btn {
        padding: 0.625rem 1.5rem;
        font-size: 0.875rem;
    }
    
    .timer-section {
        padding: 1.5rem;
    }
    
    .reminder-options {
        flex-direction: column;
        gap: 1rem;
    }
}

/* Dark Mode Support */
@media (prefers-color-scheme: dark) {
    :root {
        --bg-primary: #1f2937;
        --bg-secondary: #111827;
        --bg-tertiary: #374151;
        --text-primary: #f9fafb;
        --text-secondary: #d1d5db;
        --border-color: #4b5563;
    }
    
    .exercise-card.selected {
        background-color: rgba(79, 70, 229, 0.15);
    }
    
    .exercise-card.active {
        background-color: rgba(16, 185, 129, 0.15);
    }
    
    .btn-secondary {
        background-color: var(--bg-tertiary);
        color: var(--text-primary);
    }
    
    .btn-secondary:hover {
        background-color: #4b5563;
    }
}