/* CSS Custom Properties - Light Theme (default) */
:root {
    --color-bg: #ffffff;
    --color-bg-secondary: #f5f5f7;
    --color-bg-tertiary: #e8e8ed;
    --color-text: #1d1d1f;
    --color-text-secondary: #6e6e73;
    --color-text-tertiary: #86868b;
    --color-primary: #0071e3;
    --color-primary-hover: #0077ed;
    --color-success: #34c759;
    --color-warning: #ff9500;
    --color-danger: #ff3b30;
    --color-again: #ff3b30;
    --color-hard: #ff9500;
    --color-good: #34c759;
    --color-easy: #5856d6;
    --color-border: #d2d2d7;
    --color-card-bg: #ffffff;
    --color-card-shadow: rgba(0, 0, 0, 0.1);
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --shadow-sm: 0 1px 3px var(--color-card-shadow);
    --shadow-md: 0 4px 12px var(--color-card-shadow);
    --shadow-lg: 0 8px 24px var(--color-card-shadow);
    --transition-fast: 150ms ease;
    --transition-normal: 250ms ease;
    --transition-slow: 350ms ease;
}

/* Dark Theme */
@media (prefers-color-scheme: dark) {
    :root {
        --color-bg: #000000;
        --color-bg-secondary: #1c1c1e;
        --color-bg-tertiary: #2c2c2e;
        --color-text: #f5f5f7;
        --color-text-secondary: #a1a1a6;
        --color-text-tertiary: #6e6e73;
        --color-primary: #0a84ff;
        --color-primary-hover: #409cff;
        --color-success: #30d158;
        --color-warning: #ff9f0a;
        --color-danger: #ff453a;
        --color-again: #ff453a;
        --color-hard: #ff9f0a;
        --color-good: #30d158;
        --color-easy: #5e5ce6;
        --color-border: #38383a;
        --color-card-bg: #1c1c1e;
        --color-card-shadow: rgba(0, 0, 0, 0.3);
    }
}

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

html {
    font-size: 16px;
    -webkit-text-size-adjust: 100%;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
    background-color: var(--color-bg);
    color: var(--color-text);
    line-height: 1.5;
    min-height: 100vh;
    min-height: 100dvh;
    transition: background-color var(--transition-normal), color var(--transition-normal);
}

#app {
    display: flex;
    flex-direction: column;
    min-height: 100vh;
    min-height: 100dvh;
    max-width: 600px;
    margin: 0 auto;
    padding: 0 16px;
}

/* Header */
.header {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 16px 0;
    position: sticky;
    top: 0;
    background-color: var(--color-bg);
    z-index: 100;
    border-bottom: 1px solid var(--color-border);
}

.logo {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--color-primary);
    margin-bottom: 12px;
}

.nav {
    display: flex;
    gap: 4px;
    background-color: var(--color-bg-secondary);
    padding: 4px;
    border-radius: var(--radius-md);
    width: 100%;
}

.nav-btn {
    flex: 1;
    padding: 8px 12px;
    border: none;
    background: transparent;
    color: var(--color-text-secondary);
    font-size: 0.875rem;
    font-weight: 500;
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.nav-btn:hover {
    color: var(--color-text);
}

.nav-btn.active {
    background-color: var(--color-card-bg);
    color: var(--color-text);
    box-shadow: var(--shadow-sm);
}

/* Main Content */
.main {
    flex: 1;
    padding: 20px 0;
}

.view {
    display: none;
}

.view.active {
    display: block;
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 12px 24px;
    border: none;
    border-radius: var(--radius-md);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-fast);
    text-decoration: none;
}

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

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

.btn-primary:hover:not(:disabled) {
    background-color: var(--color-primary-hover);
}

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

.btn-secondary:hover:not(:disabled) {
    background-color: var(--color-bg-tertiary);
}

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

.btn-danger:hover:not(:disabled) {
    opacity: 0.9;
}

.btn-link {
    background: transparent;
    color: var(--color-primary);
    padding: 8px 0;
}

.btn-link:hover {
    text-decoration: underline;
}

.btn-small {
    padding: 8px 16px;
    font-size: 0.875rem;
}

.btn-large {
    width: 100%;
    padding: 16px 24px;
    font-size: 1.125rem;
}

/* Home View */
.home-header {
    text-align: center;
    margin-bottom: 24px;
}

.home-header h2 {
    font-size: 1.5rem;
    margin-bottom: 4px;
}

.subtitle {
    color: var(--color-text-secondary);
    font-size: 0.875rem;
}

.domain-list {
    display: flex;
    flex-direction: column;
    gap: 12px;
    margin-bottom: 24px;
}

.domain-card {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 16px;
    background-color: var(--color-card-bg);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.domain-card:hover {
    border-color: var(--color-primary);
}

.domain-card.selected {
    border-color: var(--color-primary);
    background-color: var(--color-bg-secondary);
}

.domain-checkbox {
    width: 24px;
    height: 24px;
    border: 2px solid var(--color-border);
    border-radius: 6px;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
    transition: all var(--transition-fast);
}

.domain-card.selected .domain-checkbox {
    background-color: var(--color-primary);
    border-color: var(--color-primary);
}

.domain-checkbox::after {
    content: '';
    width: 12px;
    height: 12px;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='white'%3E%3Cpath d='M9 16.17L4.83 12l-1.42 1.41L9 19 21 7l-1.41-1.41z'/%3E%3C/svg%3E");
    background-size: contain;
    opacity: 0;
    transition: opacity var(--transition-fast);
}

.domain-card.selected .domain-checkbox::after {
    opacity: 1;
}

.domain-info {
    flex: 1;
    min-width: 0;
}

.domain-name {
    font-weight: 600;
    font-size: 0.9375rem;
    margin-bottom: 4px;
}

.domain-meta {
    display: flex;
    gap: 12px;
    font-size: 0.75rem;
    color: var(--color-text-secondary);
}

.domain-progress-bar {
    width: 60px;
    height: 6px;
    background-color: var(--color-bg-tertiary);
    border-radius: 3px;
    overflow: hidden;
}

.domain-progress-fill {
    height: 100%;
    background-color: var(--color-success);
    border-radius: 3px;
    transition: width var(--transition-normal);
}

/* Study View */
.study-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
}

.study-progress {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
}

.flashcard-container {
    perspective: 1000px;
    margin-bottom: 20px;
}

.flashcard {
    position: relative;
    width: 100%;
    aspect-ratio: 3 / 4;
    max-height: 400px;
    cursor: pointer;
}

.flashcard-inner {
    position: relative;
    width: 100%;
    height: 100%;
    transform-style: preserve-3d;
    transition: transform 0.5s ease;
}

.flashcard.flipped .flashcard-inner {
    transform: rotateY(180deg);
}

.flashcard-front,
.flashcard-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    -webkit-backface-visibility: hidden;
    background-color: var(--color-card-bg);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-lg);
    padding: 24px;
    display: flex;
    flex-direction: column;
    box-shadow: var(--shadow-md);
    overflow-y: auto;
}

.flashcard-back {
    transform: rotateY(180deg);
}

.card-domain {
    display: inline-block;
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--color-primary);
    background-color: var(--color-bg-secondary);
    padding: 4px 8px;
    border-radius: var(--radius-sm);
    margin-bottom: 16px;
    align-self: flex-start;
}

.card-question {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    font-size: 1.125rem;
    font-weight: 500;
}

.card-answer {
    font-size: 1rem;
    line-height: 1.6;
    margin-bottom: 16px;
}

.tap-hint {
    font-size: 0.75rem;
    color: var(--color-text-tertiary);
    text-align: center;
}

.read-more-container {
    margin-top: auto;
}

.read-more-content {
    display: none;
    margin-top: 12px;
    padding-top: 12px;
    border-top: 1px solid var(--color-border);
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    line-height: 1.6;
}

.read-more-content.expanded {
    display: block;
}

/* Rating Buttons */
.rating-buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 8px;
}

.rating-buttons.hidden {
    display: none;
}

.btn-rating {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 12px 8px;
    border-radius: var(--radius-md);
    background-color: var(--color-bg-secondary);
    border: 1px solid var(--color-border);
}

.btn-rating:hover {
    transform: translateY(-2px);
}

.rating-label {
    font-weight: 600;
    font-size: 0.875rem;
}

.rating-hint {
    font-size: 0.6875rem;
    color: var(--color-text-tertiary);
    margin-top: 2px;
}

.btn-again {
    border-color: var(--color-again);
}
.btn-again .rating-label {
    color: var(--color-again);
}

.btn-hard {
    border-color: var(--color-hard);
}
.btn-hard .rating-label {
    color: var(--color-hard);
}

.btn-good {
    border-color: var(--color-good);
}
.btn-good .rating-label {
    color: var(--color-good);
}

.btn-easy {
    border-color: var(--color-easy);
}
.btn-easy .rating-label {
    color: var(--color-easy);
}

/* Session Complete */
.session-complete {
    text-align: center;
    padding: 40px 20px;
}

.session-complete.hidden {
    display: none;
}

.session-complete h2 {
    margin-bottom: 12px;
}

.session-complete p {
    color: var(--color-text-secondary);
    margin-bottom: 24px;
}

/* Stats View */
.stats-overview {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 12px;
    margin-bottom: 32px;
}

.stat-card {
    background-color: var(--color-card-bg);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    padding: 16px;
    text-align: center;
}

.stat-value {
    display: block;
    font-size: 1.75rem;
    font-weight: 700;
    color: var(--color-primary);
    margin-bottom: 4px;
}

.stat-label {
    font-size: 0.75rem;
    color: var(--color-text-secondary);
}

.domain-stats {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.domain-stat-card {
    background-color: var(--color-card-bg);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    padding: 16px;
}

.domain-stat-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 8px;
}

.domain-stat-name {
    font-weight: 600;
    font-size: 0.875rem;
}

.domain-stat-percent {
    font-size: 0.875rem;
    color: var(--color-success);
    font-weight: 600;
}

.domain-stat-bar {
    height: 8px;
    background-color: var(--color-bg-tertiary);
    border-radius: 4px;
    overflow: hidden;
    margin-bottom: 8px;
}

.domain-stat-fill {
    height: 100%;
    background-color: var(--color-success);
    border-radius: 4px;
    transition: width var(--transition-normal);
}

.domain-stat-details {
    display: flex;
    gap: 16px;
    font-size: 0.75rem;
    color: var(--color-text-secondary);
}

/* Settings View */
.settings-group {
    margin-bottom: 32px;
}

.settings-group h3 {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.5px;
    margin-bottom: 12px;
}

.setting-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 16px;
    background-color: var(--color-card-bg);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    margin-bottom: 8px;
}

.setting-item label {
    font-weight: 500;
}

.setting-item input[type="number"] {
    width: 80px;
    padding: 8px 12px;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-sm);
    background-color: var(--color-bg);
    color: var(--color-text);
    font-size: 1rem;
    text-align: center;
}

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

.about-text {
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    line-height: 1.6;
}

/* Modal */
.modal {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: rgba(0, 0, 0, 0.5);
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 20px;
    z-index: 1000;
}

.modal.hidden {
    display: none;
}

.modal-content {
    background-color: var(--color-card-bg);
    border-radius: var(--radius-lg);
    padding: 24px;
    width: 100%;
    max-width: 400px;
    max-height: 80vh;
    overflow-y: auto;
}

.modal-content h3 {
    margin-bottom: 16px;
}

.modal-content p {
    color: var(--color-text-secondary);
    margin-bottom: 16px;
}

.modal-content textarea {
    width: 100%;
    height: 150px;
    padding: 12px;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    background-color: var(--color-bg);
    color: var(--color-text);
    font-family: monospace;
    font-size: 0.75rem;
    resize: vertical;
    margin-bottom: 16px;
}

.modal-actions {
    display: flex;
    gap: 8px;
    justify-content: flex-end;
}

/* Utilities */
.hidden {
    display: none !important;
}

/* Responsive adjustments */
@media (min-width: 480px) {
    .domain-card {
        padding: 20px;
    }

    .flashcard {
        max-height: 450px;
    }
}

/* Safe area for notched devices */
@supports (padding: max(0px)) {
    #app {
        padding-left: max(16px, env(safe-area-inset-left));
        padding-right: max(16px, env(safe-area-inset-right));
        padding-bottom: max(16px, env(safe-area-inset-bottom));
    }
}