:root {
    --transition-speed: 0.3s;
    --font-stack: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
}

.theme-light {
    --bg-primary: #ffffff;
    --bg-secondary: #f4f4f6;
    --text-primary: #1c1c1e;
    --text-secondary: #8e8e93;
    --accent: #007aff;
    --accent-light: #e5f1ff;
    --border-color: #e5e5ea;
    --success: #34c759;
    --error: #ff3b30;
    --card-shadow: 0 4px 6px rgba(0, 0, 0, 0.05);
}

.theme-sepia {
    --bg-primary: #f4ecd8;
    --bg-secondary: #eadecd;
    --text-primary: #433422;
    --text-secondary: #70604c;
    --accent: #a0522d;
    --accent-light: #f5e1c8;
    --border-color: #d3c2b0;
    --success: #607d3b;
    --error: #b22222;
    --card-shadow: 0 4px 6px rgba(67, 52, 34, 0.1);
}

.theme-dark {
    --bg-primary: #121212;
    --bg-secondary: #1e1e1e;
    --text-primary: #f2f2f7;
    --text-secondary: #8e8e93;
    --accent: #0a84ff;
    --accent-light: #1c355e;
    --border-color: #38383a;
    --success: #30d158;
    --error: #ff453a;
    --card-shadow: 0 4px 6px rgba(0, 0, 0, 0.5);
}

body {
    background-color: var(--bg-primary);
    color: var(--text-primary);
    font-family: var(--font-stack);
    margin: 0;
    padding: 0;
    transition: background-color var(--transition-speed), color var(--transition-speed);
    touch-action: manipulation;
}

#app-container {
    display: flex;
    flex-direction: column;
    height: 100dvh;
    max-width: 512px;
    margin: 0 auto;
}

@media (min-width: 600px) {
    #app-container {
        border-left: 1px solid var(--border-color);
        border-right: 1px solid var(--border-color);
    }
}

#challenge-banner {
    background-color: var(--accent);
    color: #ffffff;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 8px 16px;
    font-weight: bold;
}

#challenge-banner.hidden { display: none; }

.hidden { display: none !important; }

.skip-link {
    position: absolute;
    top: -100%;
    left: 8px;
    background: var(--accent);
    color: #fff;
    padding: 8px 16px;
    border-radius: 0 0 6px 6px;
    z-index: 300;
    font-weight: 600;
    text-decoration: none;
}
.skip-link:focus {
    top: 0;
}

.app-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 12px 16px;
    padding-top: max(12px, env(safe-area-inset-top));
    background-color: var(--bg-primary);
    border-bottom: 1px solid var(--border-color);
}

.app-header h1 {
    font-size: 1.25rem;
    margin: 0;
    font-weight: 700;
}

.app-header button {
    background: none;
    border: none;
    color: var(--accent);
    font-size: 1.25rem;
    cursor: pointer;
    padding: 12px;
    min-width: 48px;
    min-height: 48px;
}

.header-actions {
    display: flex;
    gap: 8px;
    align-items: center;
}

.streak-badge {
    background: var(--accent);
    color: #fff;
    font-size: 0.75rem;
    font-weight: 700;
    padding: 4px 8px;
    border-radius: 12px;
    white-space: nowrap;
}

#game-container {
    flex: 1;
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

.scroll-container {
    flex: 1;
    overflow-y: auto;
    padding: 20px;
    display: flex;
    flex-direction: column;
    gap: 15px;
    align-items: center;
    overscroll-behavior: contain;
}

.chain-node {
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 12px 24px;
    box-shadow: var(--card-shadow);
    transform: translateY(20px);
    opacity: 0;
    animation: slideUp 0.4s forwards cubic-bezier(0.1, 0.8, 0.25, 1);
}

.chain-node .word-text {
    font-size: 1.1rem;
    font-weight: 600;
}

.chain-node.hidden { display: none; }

@keyframes slideUp {
    to {
        transform: translateY(0);
        opacity: 1;
    }
}

@media (prefers-reduced-motion: reduce) {
    .chain-node {
        animation: none;
        opacity: 1;
        transform: none;
    }
}

#input-area {
    padding: 12px 16px;
    padding-bottom: max(12px, env(safe-area-inset-bottom));
    background-color: var(--bg-primary);
    border-top: 1px solid var(--border-color);
}

.input-row {
    display: flex;
    align-items: center;
    gap: 8px;
}

#prefix-display {
    background-color: var(--accent-light);
    color: var(--accent);
    padding: 8px 12px;
    border-radius: 6px;
    font-weight: 600;
    white-space: nowrap;
}

#word-input {
    flex: 1;
    padding: 10px 12px;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    font-size: 1rem;
    font-family: var(--font-stack);
    background-color: var(--bg-secondary);
    color: var(--text-primary);
    outline: none;
}

#word-input:focus {
    border-color: var(--accent);
}

#btn-submit {
    background-color: var(--accent);
    color: #ffffff;
    border: none;
    border-radius: 6px;
    padding: 10px 18px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: opacity 0.2s;
}

#btn-submit:active {
    opacity: 0.7;
}

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

#error-message {
    margin: 8px 0 0;
    padding: 0;
    font-size: 0.875rem;
    color: var(--error);
}

#error-message.hidden { display: none; }

.app-footer {
    padding: 10px 16px;
    background-color: var(--bg-primary);
    border-top: 1px solid var(--border-color);
}

#stats-summary {
    display: flex;
    justify-content: space-between;
    font-size: 0.9rem;
    color: var(--text-secondary);
}

#stats-summary strong {
    color: var(--text-primary);
}

#modal-container {
    position: fixed;
    inset: 0;
    background-color: rgba(0, 0, 0, 0.5);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 100;
}

#modal-container.hidden { display: none; }

.modal-content {
    background-color: var(--bg-primary);
    border-radius: 12px;
    padding: 24px;
    width: min(90vw, 400px);
    max-height: 80vh;
    overflow-y: auto;
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.15);
}

.modal-content h2 {
    margin: 0 0 16px;
    color: var(--text-primary);
}

.modal-content p {
    margin: 8px 0;
    color: var(--text-secondary);
}

.modal-btn {
    display: block;
    width: 100%;
    padding: 10px 16px;
    margin: 8px 0;
    border: none;
    border-radius: 6px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    background-color: var(--accent);
    color: #ffffff;
    transition: opacity 0.2s;
}

.modal-btn:active {
    opacity: 0.7;
}

.modal-btn-secondary {
    background-color: var(--bg-secondary);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
}

.modal-content input[type="text"] {
    width: 100%;
    padding: 10px 12px;
    margin: 8px 0;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    font-size: 0.875rem;
    background-color: var(--bg-secondary);
    color: var(--text-primary);
    box-sizing: border-box;
}

/* --- Calendar --- */

.cal-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 16px;
}

.cal-header h2 {
    margin: 0;
    font-size: 1.1rem;
}

.cal-nav {
    background: none;
    border: 1px solid var(--border-color);
    border-radius: 6px;
    padding: 6px 12px;
    cursor: pointer;
    color: var(--text-primary);
    font-size: 1rem;
}

.cal-nav:active {
    opacity: 0.6;
}

.cal-grid {
    display: grid;
    grid-template-columns: repeat(7, 1fr);
    gap: 4px;
    margin-bottom: 12px;
}

.cal-day-name {
    text-align: center;
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--text-secondary);
    padding: 4px 0;
}

.cal-day {
    aspect-ratio: 1;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    border-radius: 8px;
    font-size: 0.875rem;
    font-weight: 600;
    cursor: default;
    position: relative;
    border: 2px solid transparent;
    background-color: var(--bg-secondary);
    color: var(--text-primary);
    min-width: 40px;
    min-height: 40px;
}

.cal-day[data-playable="true"] {
    cursor: pointer;
}

.cal-day[data-playable="true"]:hover {
    border-color: var(--accent);
}

.cal-empty {
    background: none;
    border: none;
    cursor: default;
}

.cal-today {
    border-color: var(--accent);
    font-weight: 700;
}

.cal-completed {
    background-color: var(--success);
    color: #ffffff;
}

.cal-unlocked {
    background-color: #ffd60a;
    color: #1c1c1e;
}

.cal-locked {
    opacity: 0.5;
}

.cal-future {
    opacity: 0.3;
}

.cal-status {
    font-size: 0.65rem;
    line-height: 1;
}

.cal-legend {
    display: flex;
    flex-wrap: wrap;
    gap: 12px;
    justify-content: center;
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin: 8px 0;
}

.cal-legend-item {
    display: inline-flex;
    align-items: center;
    gap: 4px;
}

/* --- Ad overlay --- */

.ad-simulation-overlay {
    position: fixed;
    inset: 0;
    background-color: rgba(0, 0, 0, 0.8);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 200;
}

.ad-box {
    background-color: #1c1c1e;
    border-radius: 16px;
    padding: 32px;
    text-align: center;
    color: #ffffff;
    min-width: 280px;
}

.ad-box h3 {
    margin: 0 0 20px;
    font-size: 1.1rem;
}

.ad-progress-bar {
    height: 8px;
    background-color: #38383a;
    border-radius: 4px;
    overflow: hidden;
    margin: 16px 0;
}

.progress-fill {
    height: 100%;
    width: 0%;
    background-color: var(--accent);
    transition: width 0.3s;
}

.ad-box p {
    color: #8e8e93;
    font-size: 0.9rem;
}

#loading-overlay {
    position: fixed;
    inset: 0;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    background: var(--bg-primary);
    z-index: 999;
    gap: 16px;
    font-size: 0.9rem;
    color: var(--text-secondary);
    transition: opacity 0.3s;
}
#loading-overlay.fade-out {
    opacity: 0;
    pointer-events: none;
}
.spinner {
    width: 32px;
    height: 32px;
    border: 3px solid var(--border-color);
    border-top-color: var(--accent);
    border-radius: 50%;
    animation: spin 0.7s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

.ad-banner {
    height: 50px;
    background-color: var(--bg-secondary);
    border-top: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.75rem;
    color: var(--text-secondary);
}

.premium-badge {
    background-color: #ffd60a;
    color: #1c1c1e;
    font-size: 0.6rem;
    font-weight: 700;
    padding: 2px 6px;
    border-radius: 4px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    cursor: default;
}

.premium-gate {
    filter: blur(4px);
    pointer-events: none;
    user-select: none;
}

.premium-gate-overlay {
    position: relative;
}

.premium-gate-overlay::after {
    content: '🔒 Premium';
    position: absolute;
    inset: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    background: rgba(0,0,0,0.1);
    font-weight: 700;
    font-size: 1rem;
    color: var(--accent);
    backdrop-filter: blur(2px);
}

#branching-view {
    display: flex;
    flex-wrap: wrap;
    gap: 6px;
    padding: 8px 4px 0;
    min-height: 32px;
}

#branching-view .branch-pill {
    display: inline-block;
    padding: 4px 12px;
    background: var(--accent-light);
    color: var(--accent);
    border-radius: 12px;
    font-size: 0.8rem;
    font-weight: 600;
    cursor: pointer;
    transition: transform 0.15s;
    border: 1px solid transparent;
}

#branching-view .branch-pill:hover {
    transform: scale(1.05);
    border-color: var(--accent);
}

#branching-view .branch-pill.more {
    background: var(--bg-secondary);
    color: var(--text-secondary);
    font-weight: 400;
    cursor: default;
}