:root {
    /* Light Mode — Brutalist Ink */
    --ink-black: #1A1A1A;
    --ink-gray: #3A3A3A;
    --ink-light: #5C5C5C;
    --paper-white: #EDEDED;
    --paper-gray: #DCDCDC;
    --paper-accent: #CCCCCC;

    --accent-ink: #4A4A4A;
    --accent-success: #3A3A3A;
    --accent-error: #6B6B6B;
    --accent-hint: #5C5C5C;

    --bg-primary: var(--paper-white);
    --bg-secondary: var(--paper-gray);
    --bg-elevated: #F5F5F5;
    --text-primary: var(--ink-black);
    --text-secondary: var(--ink-gray);
    --text-tertiary: var(--ink-light);
    --border-color: var(--ink-black);
    --shadow-color: rgba(0, 0, 0, 0.15);
    --shadow-offset: 4px 4px 0 rgba(0, 0, 0, 0.15);
    --pencil-color: #888888;

    --grid-size: 420px;
    --cell-size: 70px;

    /* Typography */
    --font-display: 'Space Grotesk', sans-serif;
    --font-mono: 'JetBrains Mono', monospace;

    /* Transitions — refined, not raw */
    --transition-fast: 0.15s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-medium: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 0.5s cubic-bezier(0.4, 0, 0.2, 1);
}

[data-theme="dark"] {
    --ink-black: #E0E0E0;
    --ink-gray: #B0B0B0;
    --ink-light: #808080;
    --paper-white: #1E1E1E;
    --paper-gray: #282828;
    --paper-accent: #333333;

    --accent-ink: #C0C0C0;
    --accent-success: #A0A0A0;
    --accent-error: #909090;
    --accent-hint: #909090;

    --bg-primary: var(--paper-white);
    --bg-secondary: var(--paper-gray);
    --bg-elevated: #242424;
    --text-primary: var(--ink-black);
    --text-secondary: var(--ink-gray);
    --text-tertiary: var(--ink-light);
    --border-color: var(--ink-black);
    --shadow-color: rgba(0, 0, 0, 0.4);
    --shadow-offset: 4px 4px 0 rgba(0, 0, 0, 0.35);
    --pencil-color: #999999;
}

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

body {
    font-family: var(--font-display);
    background: var(--bg-primary);
    color: var(--text-primary);
    min-height: 100vh;
    position: relative;
    transition: background var(--transition-medium), color var(--transition-medium);
    overflow-x: hidden;
}

/* Ink Texture — removed for solid background */
.ink-texture {
    display: none;
}

/* ==========================================
   HEADER — Brutalist Redesign
   ========================================== */
.header {
    background: var(--bg-primary);
    border-bottom: 3px solid var(--text-primary);
    padding: 1.25rem 2rem;
    position: sticky;
    top: 0;
    z-index: 100;
    transition: all var(--transition-medium);
}

.header-content {
    max-width: 1200px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 1.5rem;
}

.logo {
    font-size: 2.5rem;
    font-weight: 700;
    letter-spacing: -0.03em;
    text-transform: uppercase;
    position: relative;
}

.logo-ink {
    color: var(--text-primary);
    font-style: normal;
    font-weight: 700;
}

.logo-sudoku {
    color: var(--text-secondary);
    font-weight: 400;
}

.header-controls {
    display: flex;
    gap: 0.75rem;
}

.header-nav {
    display: flex;
    align-items: center;
    gap: 0.6rem;
    padding: 0.4rem;
    border: 2px solid var(--text-primary);
    border-radius: 6px;
    background: var(--bg-secondary);
    box-shadow: 3px 3px 0 var(--shadow-color);
}

.nav-link {
    text-decoration: none;
    color: var(--text-primary);
    font-family: var(--font-display);
    font-weight: 600;
    font-size: 0.95rem;
    letter-spacing: 0.06em;
    text-transform: uppercase;
    padding: 0.5rem 0.9rem;
    border-radius: 4px;
    border: 2px solid transparent;
    transition: all var(--transition-fast);
    touch-action: manipulation;
}

.nav-link:hover {
    background: var(--text-primary);
    color: var(--bg-primary);
    border-color: var(--text-primary);
    transform: translate(-1px, -1px);
}

.nav-link:active {
    transform: translate(2px, 2px);
}

.nav-link.active {
    background: var(--text-primary);
    color: var(--bg-primary);
    border-color: var(--text-primary);
    box-shadow: 2px 2px 0 var(--shadow-color);
}

.nav-link.disabled {
    opacity: 0.5;
    cursor: not-allowed;
    position: relative;
    border-color: var(--paper-accent);
    pointer-events: none;
}

.nav-link.disabled::after {
    content: '';
    position: absolute;
    left: 4px;
    right: 4px;
    top: 50%;
    height: 2px;
    background: var(--text-primary);
    transform: translateY(-50%) rotate(-8deg);
    opacity: 1;
}

.btn-icon {
    width: 44px;
    height: 44px;
    border: 2px solid var(--text-primary);
    background: var(--bg-primary);
    color: var(--text-primary);
    border-radius: 4px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all var(--transition-fast);
    position: relative;
    overflow: hidden;
    box-shadow: 3px 3px 0 var(--shadow-color);
    touch-action: manipulation;
}

.btn-icon:hover {
    background: var(--text-primary);
    color: var(--bg-primary);
    transform: translate(-1px, -1px);
    box-shadow: 4px 4px 0 var(--shadow-color);
}

.btn-icon:hover svg {
    stroke: var(--bg-primary);
}

.btn-icon:hover .lang-indicator {
    color: var(--bg-primary);
}

.btn-icon:active {
    transform: translate(2px, 2px);
    box-shadow: 1px 1px 0 var(--shadow-color);
}

.lang-indicator {
    font-family: var(--font-mono);
    font-weight: 600;
    font-size: 0.875rem;
    color: var(--text-primary);
    transition: color var(--transition-fast);
}

.icon-sun,
.icon-moon {
    transition: all var(--transition-fast);
}

[data-theme="light"] .icon-moon {
    display: none;
}

[data-theme="dark"] .icon-sun {
    display: none;
}

/* ==========================================
   MAIN CONTAINER
   ========================================== */
.main-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 3rem 2rem;
    position: relative;
    z-index: 2;
}

.game-wrapper {
    display: flex;
    flex-direction: column;
    gap: 2rem;
    animation: fadeIn var(--transition-slow);
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }

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

/* ==========================================
   GAME INFO CARDS
   ========================================== */
.game-info {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1.5rem;
}

.info-card {
    background: var(--bg-elevated);
    padding: 1.5rem;
    border-radius: 4px;
    border: 2px solid var(--text-primary);
    box-shadow: var(--shadow-offset);
    transition: all var(--transition-fast);
}

.info-card:hover {
    background: var(--bg-secondary);
}

.info-label {
    font-size: 0.8rem;
    color: var(--text-tertiary);
    text-transform: uppercase;
    letter-spacing: 0.15em;
    margin-bottom: 0.5rem;
    font-weight: 700;
}

.info-value {
    font-size: 1.75rem;
    font-weight: 700;
    color: var(--text-primary);
    font-family: var(--font-mono);
}

.info-value-inline {
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

.status-badge {
    font-size: 0.7rem;
    font-weight: 700;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    padding: 0.25rem 0.5rem;
    border: 2px solid var(--text-primary);
    border-radius: 4px;
    color: var(--text-primary);
    background: var(--bg-secondary);
    opacity: 1;
    transform: translateY(0);
    transition: opacity var(--transition-fast), transform var(--transition-fast);
}

.status-badge.status-hidden {
    opacity: 0;
    transform: translateY(-4px);
    pointer-events: none;
}

.status-badge.status-paused {
    color: var(--accent-hint);
    border-color: var(--accent-hint);
}

/* ==========================================
   SUDOKU GRID
   ========================================== */
.sudoku-container {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 2rem;
}

.sudoku-grid {
    width: var(--grid-size);
    height: var(--grid-size);
    display: grid;
    grid-template-columns: repeat(6, 1fr);
    grid-template-rows: repeat(6, 1fr);
    border: 4px solid var(--text-primary);
    border-radius: 4px;
    box-shadow: 6px 6px 0 var(--shadow-color);
    position: relative;
    overflow: hidden;
    background: var(--bg-elevated);
}

.cell {
    background: var(--bg-elevated);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.75rem;
    font-weight: 600;
    font-family: var(--font-mono);
    cursor: pointer;
    transition: all var(--transition-fast);
    position: relative;
    user-select: none;
    border: 1.5px solid var(--paper-accent);
    touch-action: manipulation;
}

.cell:hover:not(.cell-fixed) {
    background: var(--paper-gray);
}

.cell.cell-highlight {
    background: var(--paper-gray);
}

[data-theme="dark"] .cell.cell-highlight {
    background: var(--paper-accent);
}

.cell.cell-same-number {
    background: var(--paper-accent);
    font-weight: 800;
}

[data-theme="dark"] .cell.cell-same-number {
    background: #3A3A3A;
}

.cell.cell-fixed {
    color: var(--text-primary);
    cursor: default;
    font-weight: 700;
}

.cell.cell-user {
    color: var(--text-secondary);
}

.cell.cell-selected {
    background: var(--text-primary);
    color: var(--bg-elevated);
}

.cell.cell-error {
    background: #555555;
    color: var(--bg-elevated);
    animation: shake 0.3s;
}

.cell:focus-visible {
    outline: 3px solid var(--text-primary);
    outline-offset: -3px;
}

[data-theme="dark"] .cell.cell-error {
    background: #999999;
    color: var(--bg-primary);
}

.cell.cell-hint {
    animation: hintPulse 0.6s;
}

@keyframes shake {

    0%,
    100% {
        transform: translateX(0);
    }

    25% {
        transform: translateX(-4px);
    }

    75% {
        transform: translateX(4px);
    }
}

@keyframes hintPulse {

    0%,
    100% {
        transform: scale(1);
    }

    50% {
        transform: scale(1.15);
        background: var(--paper-accent);
    }
}

/* Thick borders for 3x2 box regions */
.cell.cell-box-right {
    border-right: 4px solid var(--text-primary);
}

.cell.cell-box-bottom {
    border-bottom: 4px solid var(--text-primary);
}

/* Pencil marks */
.pencil-marks {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-template-rows: repeat(2, 1fr);
    width: 100%;
    height: 100%;
    padding: 2px;
    gap: 0;
}

.pm {
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.65rem;
    font-family: var(--font-mono);
    font-weight: 600;
    color: var(--pencil-color);
    line-height: 1;
}

/* ==========================================
   TOOLS BAR
   ========================================== */
.tools-bar {
    display: flex;
    justify-content: center;
    gap: 0.75rem;
    width: 100%;
    max-width: var(--grid-size);
}

.btn-tool {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.6rem 1.25rem;
    border: 2px solid var(--text-primary);
    background: var(--bg-elevated);
    border-radius: 6px;
    font-family: var(--font-display);
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-secondary);
    cursor: pointer;
    transition: all var(--transition-fast);
    box-shadow: 3px 3px 0 var(--shadow-color);
}

.btn-tool:hover {
    background: var(--text-primary);
    color: var(--bg-elevated);
    transform: translate(-1px, -1px);
    box-shadow: 4px 4px 0 var(--shadow-color);
}

.btn-tool:hover svg {
    stroke: var(--bg-elevated);
}

.btn-tool.active {
    background: var(--text-primary);
    color: var(--bg-elevated);
    border-color: var(--text-primary);
    box-shadow: 2px 2px 0 var(--shadow-color);
}

.btn-tool.active svg {
    stroke: var(--bg-elevated);
}

/* ==========================================
   MODAL
   ========================================== */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.6);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 2000;
    opacity: 0;
    visibility: hidden;
    transition: all var(--transition-medium);
}

.modal-overlay.show {
    opacity: 1;
    visibility: visible;
}

.modal {
    background: var(--bg-elevated);
    padding: 2rem;
    border-radius: 8px;
    box-shadow: 6px 6px 0 var(--shadow-color);
    border: 3px solid var(--text-primary);
    max-width: 380px;
    width: 90%;
    transform: scale(0.9);
    transition: transform var(--transition-medium);
}

.modal-overlay.show .modal {
    transform: scale(1);
}

.modal-text {
    font-size: 1.1rem;
    font-weight: 600;
    text-align: center;
    margin-bottom: 1.5rem;
    color: var(--text-primary);
    line-height: 1.5;
}

.modal-buttons {
    display: flex;
    gap: 0.75rem;
    justify-content: center;
}

.btn-modal {
    padding: 0.75rem 1.75rem;
    border: 2px solid var(--text-primary);
    border-radius: 6px;
    font-family: var(--font-display);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-fast);
    box-shadow: 3px 3px 0 var(--shadow-color);
}

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

.btn-modal-cancel:hover {
    background: var(--text-primary);
    color: var(--bg-elevated);
    transform: translate(-1px, -1px);
    box-shadow: 4px 4px 0 var(--shadow-color);
}

.btn-modal-confirm {
    background: var(--text-primary);
    color: var(--bg-elevated);
    border-color: var(--text-primary);
}

.btn-modal-confirm:hover {
    opacity: 0.85;
    transform: translate(-1px, -1px);
    box-shadow: 4px 4px 0 var(--shadow-color);
}

/* Shortcuts List Styling */
.shortcuts-list {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
    margin-top: 0.5rem;
}

.shortcut-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 1.5rem;
    padding-bottom: 0.5rem;
    border-bottom: 1px solid var(--paper-accent);
}

.shortcut-item:last-child {
    border-bottom: none;
}

.shortcut-keys {
    display: flex;
    gap: 0.35rem;
}

.kbd {
    background: var(--text-primary);
    color: var(--bg-primary);
    padding: 0.2rem 0.5rem;
    border-radius: 4px;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    font-weight: 700;
    min-width: 1.5rem;
    text-align: center;
    box-shadow: 2px 2px 0 var(--shadow-color);
}

.shortcut-desc {
    font-size: 0.95rem;
    font-weight: 500;
    color: var(--text-secondary);
}

/* ==========================================
   NUMBER PAD
   ========================================== */
.number-pad {
    display: grid;
    grid-template-columns: repeat(7, 1fr);
    gap: 0.75rem;
    width: 100%;
    max-width: var(--grid-size);
}

.num-btn {
    aspect-ratio: 1;
    border: 2px solid var(--text-primary);
    background: var(--bg-elevated);
    border-radius: 6px;
    font-size: 1.5rem;
    font-weight: 600;
    font-family: var(--font-mono);
    color: var(--text-primary);
    cursor: pointer;
    transition: all var(--transition-fast);
    box-shadow: 3px 3px 0 var(--shadow-color);
    position: relative;
    overflow: hidden;
    touch-action: manipulation;
}

.num-btn:hover {
    background: var(--text-primary);
    color: var(--bg-elevated);
    transform: translate(-1px, -1px);
    box-shadow: 4px 4px 0 var(--shadow-color);
}

.num-btn:active {
    transform: translate(2px, 2px);
    box-shadow: 1px 1px 0 var(--shadow-color);
}

.num-btn.num-completed {
    opacity: 0.25;
    pointer-events: none;
    transform: none;
    box-shadow: none;
}

.num-btn-clear {
    background: var(--text-secondary);
    border-color: var(--text-secondary);
    color: var(--bg-elevated);
}

.num-btn-clear:hover {
    background: var(--text-primary);
    border-color: var(--text-primary);
}

/* ==========================================
   GAME CONTROLS
   ========================================== */
.game-controls {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.difficulty-selector {
    display: flex;
    gap: 0.75rem;
    background: var(--bg-secondary);
    padding: 0.5rem;
    border-radius: 6px;
    border: 2px solid var(--text-primary);
}

.btn-difficulty {
    flex: 1;
    padding: 1rem 0.5rem;
    border: none;
    background: transparent;
    color: var(--text-secondary);
    font-family: var(--font-display);
    font-size: 0.95rem;
    font-weight: 600;
    cursor: pointer;
    border-radius: 4px;
    transition: all var(--transition-fast);
}

.btn-difficulty:hover {
    background: var(--paper-accent);
    color: var(--text-primary);
}

.btn-difficulty.active {
    background: var(--text-primary);
    color: var(--bg-elevated);
    box-shadow: 2px 2px 0 var(--shadow-color);
}

.action-buttons {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 1rem;
}

.btn-action {
    padding: 1rem 1.5rem;
    border: 2px solid var(--text-primary);
    background: var(--bg-elevated);
    color: var(--text-primary);
    font-family: var(--font-display);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    border-radius: 6px;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    transition: all var(--transition-fast);
    box-shadow: 3px 3px 0 var(--shadow-color);
    touch-action: manipulation;
}

.btn-action:hover {
    background: var(--text-primary);
    color: var(--bg-elevated);
    transform: translate(-1px, -1px);
    box-shadow: 4px 4px 0 var(--shadow-color);
}

.btn-action:hover svg {
    stroke: var(--bg-elevated);
}

.btn-action:active {
    transform: translate(2px, 2px);
    box-shadow: 1px 1px 0 var(--shadow-color);
}

.btn-hint:hover {
    background: var(--text-primary);
    border-color: var(--text-primary);
    color: var(--bg-elevated);
}

.btn-validate:hover {
    background: var(--text-primary);
    border-color: var(--text-primary);
    color: var(--bg-elevated);
}

.btn-new:hover {
    background: var(--text-primary);
    border-color: var(--text-primary);
    color: var(--bg-elevated);
}

/* ==========================================
   FOOTER
   ========================================== */
.footer {
    text-align: center;
    padding: 2rem 1.5rem;
    margin-top: 3rem;
    border-top: 3px solid var(--text-primary);
    font-family: var(--font-display);
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-tertiary);
    letter-spacing: 0.05em;
}

.footer-row {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 1rem;
    flex-wrap: wrap;
}

.footer-badge {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.35rem 0.6rem;
    border: 2px solid var(--text-primary);
    border-radius: 6px;
    background: var(--bg-elevated);
    font-size: 0.75rem;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--text-primary);
    box-shadow: 2px 2px 0 var(--shadow-color);
}

.android-icon {
    stroke: currentColor;
}

.footer-link {
    color: var(--text-primary);
    text-decoration: none;
    border-bottom: 2px solid var(--text-primary);
    padding-bottom: 1px;
    transition: color var(--transition-fast), border-color var(--transition-fast);
}

.footer-link:hover {
    color: #F5CB5C;
    border-color: #F5CB5C;
}

[data-theme="light"] .footer-link:hover {
    color: #C9A227;
    border-color: #C9A227;
}

/* ==========================================
   NOTIFICATION
   ========================================== */
.notification {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
    padding: 1rem 1.5rem;
    background: var(--bg-elevated);
    border: 2px solid var(--text-primary);
    border-radius: 4px;
    box-shadow: var(--shadow-offset);
    font-family: var(--font-display);
    font-weight: 600;
    transform: translateY(150%);
    opacity: 0;
    transition: all var(--transition-medium);
    z-index: 1000;
    max-width: 350px;
}

.notification.show {
    transform: translateY(0);
    opacity: 1;
}

.notification.success {
    border-top: 5px solid var(--text-primary);
}

.notification.error {
    border-top: 5px solid var(--text-secondary);
}

.notification.info {
    border-top: 5px solid var(--text-tertiary);
}

/* ==========================================
   RESPONSIVE
   ========================================== */
@media (min-width: 1024px) {
    .game-wrapper {
        display: grid;
        grid-template-columns: 240px 1fr 240px;
        gap: 3rem;
        align-items: start;
        max-width: 1100px;
        margin: 0 auto;
    }

    .game-info {
        grid-template-columns: 1fr;
        position: sticky;
        top: 120px;
    }

    .game-controls {
        position: sticky;
        top: 120px;
    }

    .sudoku-container {
        grid-column: 2;
    }
}

@media (max-width: 768px) {
    :root {
        --grid-size: 90vw;
        --cell-size: calc(90vw / 6);
    }

    .header {
        padding: 1rem 1.5rem;
    }

    .logo {
        font-size: 1.75rem;
    }

    .main-container {
        padding: 2rem 1rem;
    }

    .header-content {
        flex-wrap: wrap;
    }

    .header-nav {
        order: 3;
        width: 100%;
        justify-content: center;
        flex-wrap: wrap;
    }

    .game-info {
        grid-template-columns: repeat(2, 1fr);
        gap: 0.75rem;
    }

    .game-info .info-card:last-child {
        grid-column: span 2;
    }

    .difficulty-selector {
        flex-direction: row;
        flex-wrap: wrap;
    }

    .btn-difficulty {
        padding: 0.75rem 0.5rem;
        font-size: 0.9rem;
    }

    .action-buttons {
        grid-template-columns: repeat(2, 1fr);
        gap: 0.75rem;
    }

    .btn-action.btn-new {
        grid-column: span 2;
    }

    .number-pad {
        gap: 0.5rem;
    }

    .num-btn {
        font-size: 1.25rem;
    }

    .notification {
        bottom: 1rem;
        right: 1rem;
        left: 1rem;
    }
}

/* ==========================================
   LOADING STATE
   ========================================== */
.loading {
    pointer-events: none;
    opacity: 0.6;
}

.loading::after {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 40px;
    height: 40px;
    margin: -20px 0 0 -20px;
    border: 3px solid var(--text-tertiary);
    border-top-color: var(--text-primary);
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
}

@keyframes spin {
    to {
        transform: rotate(360deg);
    }
}