:root {
    /* Dark Theme (Default) */
    --bg-color: #0f172a;
    --bg-gradient-start: #1e293b;
    --bg-gradient-end: #0f172a;
    --card-bg: rgba(255, 255, 255, 0.05);
    --card-border: rgba(255, 255, 255, 0.1);
    --card-hover: rgba(255, 255, 255, 0.15);
    --accent-color: #38bdf8;
    --accent-glow: rgba(56, 189, 248, 0.5);
    --error-color: #ef4444;
    --error-bg: rgba(239, 68, 68, 0.15);
    --success-color: #10b981;
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --panel-shadow: rgba(0, 0, 0, 0.5);
}

[data-theme="light"] {
    /* Light Theme */
    --bg-color: #f1f5f9;
    --bg-gradient-start: #ffffff;
    --bg-gradient-end: #e2e8f0;
    --card-bg: rgba(255, 255, 255, 0.7);
    --card-border: rgba(148, 163, 184, 0.3);
    --card-hover: rgba(255, 255, 255, 0.9);
    --accent-color: #2563eb;
    --accent-glow: rgba(37, 99, 235, 0.3);
    --error-color: #dc2626;
    --error-bg: rgba(220, 38, 38, 0.15);
    --success-color: #059669;
    --text-primary: #0f172a;
    --text-secondary: #475569;
    --panel-shadow: rgba(0, 0, 0, 0.1);
}

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

body {
    background-color: var(--bg-color);
    background-image: radial-gradient(circle at top right, var(--bg-gradient-start) 0%, var(--bg-gradient-end) 100%);
    color: var(--text-primary);
    font-family: 'Outfit', sans-serif;
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    overflow-x: hidden;
    transition: background-color 0.4s ease, color 0.4s ease;
}

.app-container {
    width: 100%;
    max-width: 1100px;
    padding: 2rem;
    display: flex;
    flex-direction: column;
    gap: 2rem;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 1rem;
    padding-bottom: 1.5rem;
    border-bottom: 1px solid var(--card-border);
}

.header-left .title-group {
    display: flex;
    align-items: center;
    gap: 1rem;
    margin-bottom: 0.25rem;
}

.icon-btn {
    background: var(--card-bg);
    border: 1px solid var(--card-border);
    color: var(--text-primary);
    width: 40px;
    height: 40px;
    border-radius: 50%;
    display: flex;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    transition: all 0.3s ease;
}

.icon-btn:hover {
    background: var(--card-hover);
    transform: rotate(15deg);
}

.header-left h1 {
    font-size: 2.5rem;
    font-weight: 800;
    background: linear-gradient(to right, var(--accent-color), #818cf8);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}

.subtitle {
    color: var(--text-secondary);
    font-size: 1rem;
}

.header-right {
    display: flex;
    align-items: center;
    gap: 2rem;
    flex-wrap: wrap;
}

.stats {
    display: flex;
    gap: 1.5rem;
}

.stat-box {
    display: flex;
    flex-direction: column;
    align-items: center;
    background: var(--card-bg);
    padding: 0.75rem 1.5rem;
    border-radius: 12px;
    border: 1px solid var(--card-border);
    backdrop-filter: blur(10px);
}

.stat-box .label {
    font-size: 0.75rem;
    text-transform: uppercase;
    letter-spacing: 1px;
    color: var(--text-secondary);
}

.stat-box span:last-child {
    font-size: 1.5rem;
    font-weight: 700;
}

.primary-btn {
    background: linear-gradient(135deg, var(--accent-color) 0%, #3b82f6 100%);
    color: white;
    border: none;
    padding: 0.75rem 1.5rem;
    border-radius: 8px;
    font-family: inherit;
    font-weight: 600;
    font-size: 1rem;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: 0 4px 15px rgba(59, 130, 246, 0.3);
}

.primary-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(59, 130, 246, 0.5);
}

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

.glass-panel {
    background: var(--card-bg);
    border: 1px solid var(--card-border);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border-radius: 20px;
    padding: 2rem;
    box-shadow: 0 25px 50px -12px var(--panel-shadow);
}

/* Layout for Board + Sidebar */
.game-layout {
    display: grid;
    grid-template-columns: 2fr 1fr;
    gap: 2rem;
    align-items: start;
}

@media (max-width: 900px) {
    .game-layout {
        grid-template-columns: 1fr;
    }
}

.board-container {
    position: relative;
}

#game-board {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(70px, 1fr));
    gap: 1rem;
    min-height: 400px;
    transition: all 0.5s ease;
}

.card {
    aspect-ratio: 1;
    background: var(--card-bg);
    border: 1px solid var(--card-border);
    border-radius: 12px;
    display: flex;
    justify-content: center;
    align-items: center;
    font-family: 'Noto Sans JP', sans-serif;
    font-size: 2.5rem;
    color: var(--text-primary);
    cursor: pointer;
    transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.05);
    user-select: none;
}

.card:hover {
    background: var(--card-hover);
    transform: translateY(-4px);
    border-color: var(--accent-color);
    box-shadow: 0 10px 15px rgba(0, 0, 0, 0.1);
}

.card.selected {
    background: rgba(56, 189, 248, 0.15);
    border-color: var(--accent-color);
    box-shadow: 0 0 20px var(--accent-glow);
    transform: scale(1.05);
}

.card.matched {
    animation: matchAnim 0.5s forwards;
    pointer-events: none;
}

.card.error {
    animation: shake 0.4s cubic-bezier(.36, .07, .19, .97) both;
    background: var(--error-bg);
    border-color: var(--error-color);
}

/* Info Sidebar */
.info-sidebar {
    position: sticky;
    top: 2rem;
    height: fit-content;
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.info-sidebar h3 {
    font-size: 1.25rem;
    color: var(--text-secondary);
    border-bottom: 1px solid var(--card-border);
    padding-bottom: 0.5rem;
}

.kanji-info.empty {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 250px;
    text-align: center;
}

.placeholder-text {
    color: var(--text-secondary);
    font-style: italic;
    font-size: 0.95rem;
}

.details-content {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
    animation: fadeIn 0.4s ease;
}

.kanji-large {
    font-family: 'Noto Sans JP', sans-serif;
    font-size: 6rem;
    line-height: 1;
    text-align: center;
    color: var(--text-primary);
    background: linear-gradient(135deg, var(--accent-color), #818cf8);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    padding: 1rem 0;
}

.info-group {
    display: flex;
    flex-direction: column;
    gap: 1rem;
    background: rgba(0, 0, 0, 0.05);
    padding: 1rem;
    border-radius: 8px;
    border: 1px solid var(--card-border);
}

[data-theme="dark"] .info-group {
    background: rgba(255, 255, 255, 0.02);
}

.info-section {
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
}

.info-label {
    font-size: 0.75rem;
    text-transform: uppercase;
    font-weight: 700;
    color: var(--text-secondary);
    letter-spacing: 0.5px;
}

.info-value {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text-primary);
}

.info-value.meaning {
    font-size: 1.5rem;
    color: var(--accent-color);
}

.info-value.reading {
    font-family: 'Noto Sans JP', sans-serif;
}

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

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

@keyframes matchAnim {
    0% {
        transform: scale(1.05);
        opacity: 1;
    }

    50% {
        transform: scale(1.2);
        opacity: 0.8;
    }

    100% {
        transform: scale(0);
        opacity: 0;
        visibility: hidden;
    }
}

@keyframes shake {

    10%,
    90% {
        transform: translate3d(-1px, 0, 0);
    }

    20%,
    80% {
        transform: translate3d(2px, 0, 0);
    }

    30%,
    50%,
    70% {
        transform: translate3d(-4px, 0, 0);
    }

    40%,
    60% {
        transform: translate3d(4px, 0, 0);
    }
}

/* Victory Overlay */
#victory-overlay {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    border-radius: 20px;
    background: rgba(15, 23, 42, 0.8);
    backdrop-filter: blur(8px);
    z-index: 10;
    opacity: 1;
    transition: opacity 0.4s ease;
}

[data-theme="light"] #victory-overlay {
    background: rgba(255, 255, 255, 0.8);
}

#victory-overlay.hidden {
    opacity: 0;
    pointer-events: none;
}

.victory-content {
    text-align: center;
    transform: scale(1);
    transition: transform 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

#victory-overlay.hidden .victory-content {
    transform: scale(0.8);
}

.victory-content h2 {
    font-size: 2.5rem;
    color: var(--success-color);
    margin-bottom: 1rem;
}

.victory-content p {
    font-size: 1.2rem;
    margin-bottom: 0.5rem;
    color: var(--text-secondary);
}

.victory-content button {
    margin-top: 1.5rem;
}

@media (max-width: 600px) {
    .app-container {
        padding: 1rem;
    }

    .card {
        font-size: 2rem;
    }

    #game-board {
        grid-template-columns: repeat(auto-fill, minmax(50px, 1fr));
        gap: 0.5rem;
        padding: 1rem;
    }
}