/* Sudoku 365 - Styles
   Size: ~11KB uncompressed
   Performance optimized with GPU-friendly animations */

:root {
    /* Design tokens */
    --bg: #0d1117;
    --bg-secondary: #161b22;
    --bg-tertiary: #21262d;
    --text: #c9d1d9;
    --text-secondary: #8b949e;
    --text-dim: #484f58;
    --accent: #4ecdc4;
    --accent-dim: #3ca39c;
    --accent-light: #6eddd5;
    --error: #f85149;
    --success: #56d364;
    --warning: #e3b341;
    --border: #30363d;
    --border-light: #484f58;
    
    /* Spacing scale */
    --space-xs: 4px;
    --space-sm: 8px;
    --space-md: 16px;
    --space-lg: 24px;
    --space-xl: 32px;
    --space-2xl: 48px;
    
    /* Typography */
    --font-stack: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif;
    --font-mono: "SF Mono", "Monaco", "Inconsolata", "Fira Code", "Fira Mono", "Droid Sans Mono", "Courier New", monospace;
    
    /* Shadows */
    --shadow-sm: 0 1px 2px rgba(0,0,0,0.3);
    --shadow-md: 0 4px 6px rgba(0,0,0,0.4);
    --shadow-lg: 0 10px 15px rgba(0,0,0,0.5);
    
    /* Animations */
    --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-base: 250ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 350ms cubic-bezier(0.4, 0, 0.2, 1);
    
    /* Borders */
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
}

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

html {
    font-family: var(--font-stack);
    font-size: 16px;
    line-height: 1.5;
    color: var(--text);
    background: var(--bg);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    scroll-behavior: smooth;
}

body {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    overflow-x: hidden;
}

/* Accessibility */
.skip-link {
    position: absolute;
    top: -40px;
    left: 0;
    background: var(--accent);
    color: var(--bg);
    padding: var(--space-sm) var(--space-md);
    text-decoration: none;
    z-index: 100;
    border-radius: 0 0 var(--radius-md) 0;
}

.skip-link:focus {
    top: 0;
}

.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

/* Focus styles */
:focus-visible {
    outline: 2px solid var(--accent);
    outline-offset: 2px;
}

button:focus-visible {
    outline-offset: 0;
}

/* Header */
header {
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border);
    position: sticky;
    top: 0;
    z-index: 50;
    backdrop-filter: blur(10px);
}

.header-content {
    max-width: 1200px;
    margin: 0 auto;
    padding: var(--space-md);
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: var(--space-lg);
}

.logo-title {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
}

.logo {
    flex-shrink: 0;
}

h1 {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--text);
}

nav {
    display: flex;
    gap: var(--space-xs);
}

.nav-link {
    padding: var(--space-sm) var(--space-md);
    color: var(--text-secondary);
    text-decoration: none;
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
    font-weight: 500;
}

.nav-link:hover {
    color: var(--text);
    background: var(--bg-tertiary);
}

.nav-link.active {
    color: var(--accent);
    background: rgba(78, 205, 196, 0.1);
}

/* Main content */
main {
    flex: 1;
    max-width: 1200px;
    width: 100%;
    margin: 0 auto;
    padding: var(--space-lg) var(--space-md);
}

.content-section {
    display: none;
    animation: fadeIn var(--transition-base);
}

.content-section.active {
    display: block;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

h2 {
    font-size: 2rem;
    font-weight: 600;
    margin-bottom: var(--space-lg);
    color: var(--text);
}

h3 {
    font-size: 1.25rem;
    font-weight: 600;
    margin: var(--space-lg) 0 var(--space-md);
    color: var(--text);
}

/* Game Container */
.game-container {
    max-width: 600px;
    margin: 0 auto;
}

/* Game Controls Top */
.game-controls-top {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--space-lg);
    gap: var(--space-md);
    flex-wrap: wrap;
}

.difficulty-selector {
    display: flex;
    gap: var(--space-xs);
    background: var(--bg-secondary);
    padding: var(--space-xs);
    border-radius: var(--radius-md);
}

.difficulty-btn {
    padding: var(--space-sm) var(--space-md);
    background: transparent;
    color: var(--text-secondary);
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-weight: 500;
    transition: all var(--transition-fast);
    min-width: 80px;
}

.difficulty-btn:hover {
    background: var(--bg-tertiary);
    color: var(--text);
}

.difficulty-btn.active {
    background: var(--accent);
    color: var(--bg);
}

.daily-toggle {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    padding: var(--space-sm) var(--space-md);
    background: var(--bg-secondary);
    color: var(--text-secondary);
    border: 2px solid transparent;
    border-radius: var(--radius-md);
    cursor: pointer;
    font-weight: 500;
    transition: all var(--transition-fast);
}

.daily-toggle:hover {
    background: var(--bg-tertiary);
    color: var(--text);
}

.daily-toggle[aria-pressed="true"] {
    border-color: var(--accent);
    color: var(--accent);
    background: rgba(78, 205, 196, 0.1);
}

/* Sudoku Board */
.game-board-wrapper {
    display: flex;
    justify-content: center;
    margin-bottom: var(--space-lg);
}

.sudoku-board {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    grid-template-rows: repeat(9, 1fr);
    gap: 1px;
    background: var(--border);
    border: 3px solid var(--border);
    border-radius: var(--radius-md);
    width: min(100%, 540px);
    aspect-ratio: 1;
    position: relative;
}

.sudoku-cell {
    background: var(--bg);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: clamp(1.25rem, 4vw, 1.75rem);
    font-weight: 600;
    cursor: pointer;
    position: relative;
    transition: background-color var(--transition-fast);
    min-height: 44px;
    min-width: 44px;
}

/* 3x3 box borders */
.sudoku-cell:nth-child(3n) {
    border-right: 2px solid var(--border);
}

.sudoku-cell:nth-child(n+19):nth-child(-n+27),
.sudoku-cell:nth-child(n+46):nth-child(-n+54) {
    border-bottom: 2px solid var(--border);
}

.sudoku-cell.selected {
    background: rgba(78, 205, 196, 0.15);
}

.sudoku-cell.highlighted {
    background: var(--bg-tertiary);
}

.sudoku-cell.same-number {
    background: rgba(78, 205, 196, 0.08);
}

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

.sudoku-cell.error {
    color: var(--error);
    animation: shake 300ms;
}

@keyframes shake {
    0%, 100% { transform: translateX(0); }
    25% { transform: translateX(-2px); }
    75% { transform: translateX(2px); }
}

.sudoku-cell.hint {
    animation: pulse 1s ease-in-out;
}

@keyframes pulse {
    0%, 100% { background: var(--bg); }
    50% { background: rgba(78, 205, 196, 0.3); }
}

/* Notes in cells */
.cell-notes {
    position: absolute;
    inset: 2px;
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-template-rows: repeat(3, 1fr);
    gap: 0;
    pointer-events: none;
}

.note-number {
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.5em;
    color: var(--text-dim);
    font-weight: normal;
}

/* Game Controls Bottom */
.game-controls-bottom {
    display: flex;
    justify-content: space-between;
    gap: var(--space-md);
    margin-bottom: var(--space-lg);
    flex-wrap: wrap;
}

.control-group {
    display: flex;
    gap: var(--space-xs);
    flex-wrap: wrap;
}

.control-btn {
    display: flex;
    align-items: center;
    gap: var(--space-xs);
    padding: var(--space-sm) var(--space-md);
    background: var(--bg-secondary);
    color: var(--text-secondary);
    border: 2px solid transparent;
    border-radius: var(--radius-md);
    cursor: pointer;
    font-weight: 500;
    transition: all var(--transition-fast);
    min-height: 44px;
}

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

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

.control-btn.toggle[aria-pressed="true"] {
    border-color: var(--accent);
    color: var(--accent);
    background: rgba(78, 205, 196, 0.1);
}

/* Number Pad */
.number-pad {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    gap: var(--space-xs);
    margin-bottom: var(--space-lg);
}

.number-btn {
    aspect-ratio: 1;
    min-height: 44px;
    background: var(--bg-secondary);
    color: var(--text);
    border: 2px solid transparent;
    border-radius: var(--radius-md);
    font-size: 1.25rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.number-btn:hover {
    background: var(--bg-tertiary);
    transform: scale(1.05);
}

.number-btn:active {
    transform: scale(0.95);
}

.number-btn.active {
    background: var(--accent);
    color: var(--bg);
    border-color: var(--accent);
}

/* Status Bar */
.status-bar {
    display: flex;
    justify-content: space-between;
    gap: var(--space-md);
    padding: var(--space-md);
    background: var(--bg-secondary);
    border-radius: var(--radius-md);
    flex-wrap: wrap;
}

.status-item {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
}

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

.status-value {
    color: var(--text);
    font-weight: 600;
    font-family: var(--font-mono);
}

.seed-btn {
    display: flex;
    align-items: center;
    gap: var(--space-xs);
    padding: var(--space-xs) var(--space-sm);
    background: var(--bg-tertiary);
    color: var(--text);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.seed-btn:hover {
    background: var(--accent);
    color: var(--bg);
    border-color: var(--accent);
}

.seed-value {
    font-family: var(--font-mono);
    font-size: 0.875rem;
}

/* Content Sections */
.how-to-content,
.about-content,
.contact-content {
    max-width: 800px;
    margin: 0 auto;
}

p {
    margin-bottom: var(--space-md);
    line-height: 1.6;
    color: var(--text-secondary);
}

.rules-diagram {
    display: flex;
    justify-content: center;
    margin: var(--space-xl) 0;
}

.diagram {
    max-width: 300px;
    width: 100%;
    height: auto;
}

.keyboard-shortcuts ul,
.features-list ul {
    list-style: none;
    padding: 0;
}

.keyboard-shortcuts li,
.features-list li {
    padding: var(--space-sm) 0;
    color: var(--text-secondary);
    display: flex;
    align-items: center;
    gap: var(--space-sm);
}

.keyboard-shortcuts li::before,
.features-list li::before {
    content: "→";
    color: var(--accent);
    font-weight: bold;
}

kbd {
    display: inline-block;
    padding: 2px 6px;
    background: var(--bg-tertiary);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    font-family: var(--font-mono);
    font-size: 0.875rem;
    color: var(--text);
}

/* Contact Form */
.contact-form {
    background: var(--bg-secondary);
    padding: var(--space-xl);
    border-radius: var(--radius-lg);
    margin: var(--space-xl) 0;
}

.form-group {
    margin-bottom: var(--space-lg);
}

.form-group label {
    display: block;
    margin-bottom: var(--space-sm);
    color: var(--text);
    font-weight: 500;
}

.form-group input,
.form-group textarea {
    width: 100%;
    padding: var(--space-sm) var(--space-md);
    background: var(--bg);
    color: var(--text);
    border: 2px solid var(--border);
    border-radius: var(--radius-md);
    font-family: inherit;
    font-size: 1rem;
    transition: border-color var(--transition-fast);
}

.form-group input:focus,
.form-group textarea:focus {
    border-color: var(--accent);
    outline: none;
}

.submit-btn {
    padding: var(--space-md) var(--space-xl);
    background: var(--accent);
    color: var(--bg);
    border: none;
    border-radius: var(--radius-md);
    font-weight: 600;
    font-size: 1rem;
    cursor: pointer;
    transition: all var(--transition-fast);
}

.submit-btn:hover {
    background: var(--accent-light);
    transform: translateY(-1px);
}

.privacy-note {
    display: flex;
    align-items: flex-start;
    gap: var(--space-sm);
    margin-top: var(--space-lg);
    padding: var(--space-md);
    background: var(--bg);
    border-radius: var(--radius-md);
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.contact-alternative {
    text-align: center;
    margin-top: var(--space-xl);
}

.email-link {
    color: var(--accent);
    text-decoration: none;
    font-weight: 500;
    font-size: 1.125rem;
}

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

/* Footer */
footer {
    background: var(--bg-secondary);
    border-top: 1px solid var(--border);
    padding: var(--space-lg) var(--space-md);
    margin-top: auto;
}

.footer-content {
    max-width: 1200px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: var(--space-md);
    flex-wrap: wrap;
}

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

.footer-links {
    display: flex;
    align-items: center;
    gap: var(--space-md);
}

.footer-links a {
    color: var(--text-secondary);
    text-decoration: none;
    transition: color var(--transition-fast);
}

.footer-links a:hover {
    color: var(--accent);
}

.separator {
    color: var(--text-dim);
}

/* Toast Notifications */
.toast-container {
    position: fixed;
    bottom: var(--space-lg);
    right: var(--space-lg);
    z-index: 100;
    display: flex;
    flex-direction: column;
    gap: var(--space-sm);
    pointer-events: none;
}

.toast {
    padding: var(--space-md) var(--space-lg);
    background: var(--bg-secondary);
    color: var(--text);
    border-left: 4px solid var(--accent);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-lg);
    animation: slideIn var(--transition-base);
    pointer-events: auto;
}

.toast.error {
    border-left-color: var(--error);
}

.toast.success {
    border-left-color: var(--success);
}

@keyframes slideIn {
    from {
        transform: translateX(100%);
        opacity: 0;
    }
    to {
        transform: translateX(0);
        opacity: 1;
    }
}

/* Responsive Design */
@media (max-width: 768px) {
    .header-content {
        flex-direction: column;
        gap: var(--space-md);
    }
    
    nav {
        width: 100%;
        justify-content: space-around;
    }
    
    .nav-link {
        padding: var(--space-xs) var(--space-sm);
        font-size: 0.875rem;
    }
    
    h2 {
        font-size: 1.5rem;
    }
    
    .game-controls-top {
        justify-content: center;
    }
    
    .difficulty-selector {
        order: 2;
        width: 100%;
        justify-content: space-between;
    }
    
    .daily-toggle {
        order: 1;
        width: 100%;
        justify-content: center;
    }
    
    .number-pad {
        grid-template-columns: repeat(5, 1fr);
    }
    
    .control-group {
        width: 100%;
        justify-content: space-around;
    }
    
    .status-bar {
        justify-content: space-around;
    }
    
    .toast-container {
        bottom: var(--space-md);
        right: var(--space-md);
        left: var(--space-md);
    }
}

@media (max-width: 480px) {
    main {
        padding: var(--space-md) var(--space-sm);
    }
    
    .sudoku-cell {
        font-size: 1rem;
    }
    
    .number-pad {
        grid-template-columns: repeat(3, 1fr);
    }
    
    .control-btn {
        padding: var(--space-xs) var(--space-sm);
        font-size: 0.875rem;
    }
    
    .status-item {
        flex-direction: column;
        align-items: flex-start;
        gap: 0;
    }
}

/* Reduced Motion */
@media (prefers-reduced-motion: reduce) {
    *, *::before, *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
        scroll-behavior: auto !important;
    }
}

/* Print styles */
@media print {
    body {
        background: white;
        color: black;
    }
    
    header, footer, .game-controls-top, .game-controls-bottom, 
    .number-pad, .status-bar, nav {
        display: none;
    }
    
    .sudoku-board {
        border-color: black;
        background: white;
    }
    
    .sudoku-cell {
        background: white;
        color: black;
    }
}