:root {
    /* Color Palette */
    --color-primary: #1e293b;
    --color-primary-dark: #0f172a;
    --color-primary-light: #334155;
    
    --color-accent: #3b82f6;
    --color-accent-dark: #2563eb;
    --color-accent-light: #60a5fa;
    
    --color-background: #ffffff;
    --color-surface: #f8fafc;
    --color-surface-dark: #f1f5f9;
    
    --color-text-primary: #0f172a;
    --color-text-secondary: #64748b;
    --color-text-tertiary: #94a3b8;
    
    --color-border: #e2e8f0;
    --color-border-light: #f1f5f9;
    
    --color-success: #10b981;
    --color-success-bg: #d1fae5;
    --color-error: #ef4444;
    --color-error-bg: #fee2e2;
    --color-info: #3b82f6;
    --color-info-bg: #dbeafe;
    
    /* Typography */
    --font-display: 'Cormorant Garamond', serif;
    --font-body: 'Archivo', sans-serif;
    
    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 0.75rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    
    /* Shadows */
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    
    /* Border Radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    
    /* Transitions */
    --transition-base: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-fast: all 0.15s cubic-bezier(0.4, 0, 0.2, 1);

    /* board cell size — overridden at breakpoints */
    --cell-size: 70px;
}

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

body {
    font-family: var(--font-body);
    background: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
    color: var(--color-text-primary);
    min-height: 100vh;
    padding: var(--spacing-xl);
    position: relative;
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* grain Texture Overlay */
.grain-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
    opacity: 0.03;
    z-index: 1;
    background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 400 400' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='noiseFilter'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='4' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23noiseFilter)'/%3E%3C/svg%3E");
}

.container {
    max-width: 1600px;
    margin: 0 auto;
    position: relative;
    z-index: 2;
}

/* header */
.header {
    text-align: center;
    margin-bottom: var(--spacing-2xl);
    animation: fadeInDown 0.8s cubic-bezier(0.4, 0, 0.2, 1);
}

.title {
    font-family: var(--font-display);
    font-size: clamp(1.8rem, 5vw, 4rem);
    font-weight: 700;
    color: var(--color-primary);
    margin-bottom: var(--spacing-sm);
    letter-spacing: -0.02em;
    line-height: 1.1;
}

.subtitle {
    font-family: var(--font-body);
    font-size: 0.875rem;
    font-weight: 400;
    color: var(--color-text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.15em;
}

.layout {
    display: grid;
    grid-template-columns: 320px 1fr 320px;
    gap: var(--spacing-2xl);
    align-items: start;
    animation: fadeIn 1s cubic-bezier(0.4, 0, 0.2, 1) 0.2s both;
}

/* large desktop only: slightly tighter columns */
@media (max-width: 1400px) {
    .layout {
        grid-template-columns: 300px 1fr 260px;
        gap: var(--spacing-xl);
    }
}

/* tablet landscape: 2-col, info panel goes below */
@media (max-width: 1200px) {
    .layout {
        grid-template-columns: 260px 1fr;
        gap: var(--spacing-xl);
    }

    .info-panel {
        grid-column: 1 / -1;
        display: grid;
        grid-template-columns: 1fr 1fr;
        gap: var(--spacing-xl);
        align-items: start;
    }

    .info-panel .divider {
        display: none;
    }

    .info-panel .section-title {
        grid-column: 1 / -1;
        margin-bottom: 0;
    }
}

/* tablet portrait: single column, natural stacking */
@media (max-width: 900px) {
    body {
        padding: var(--spacing-lg);
    }

    .layout {
        grid-template-columns: 1fr;
        gap: var(--spacing-xl);
    }

    .control-panel { order: 1; }
    .board-wrapper  { order: 2; }
    .info-panel     { order: 3; display: block; }

    /* date controls side-by-side on tablet */
    .control-panel {
        display: grid;
        grid-template-columns: repeat(3, 1fr);
        gap: var(--spacing-md);
        align-items: start;
    }

    .control-panel .section-title {
        grid-column: 1 / -1;
        margin-bottom: 0;
    }

    .control-panel .divider {
        grid-column: 1 / -1;
        margin: var(--spacing-sm) 0;
    }

    .control-panel .action-section {
        grid-column: 1 / -1;
        display: grid;
        grid-template-columns: 1fr 1fr;
        gap: var(--spacing-sm);
    }

    .control-panel .action-section .btn {
        margin-bottom: 0;
    }

    /* the message takes full width */
    .control-panel .action-section #message {
        grid-column: 1 / -1;
        margin-top: 0;
    }

    --cell-size: 62px;
}

/* mobile: small phones */
@media (max-width: 600px) {
    body {
        padding: var(--spacing-md);
    }

    .header {
        margin-bottom: var(--spacing-xl);
    }

    /* back to stacked date controls */
    .control-panel {
        grid-template-columns: 1fr;
    }

    .control-panel .action-section {
        grid-template-columns: 1fr 1fr;
    }

    --cell-size: 44px;
}

/* very small phones */
@media (max-width: 420px) {
    body {
        padding: var(--spacing-xs) var(--spacing-sm);
    }

    --cell-size: 38px;
}

.section-title {
    font-family: var(--font-display);
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--color-primary);
    margin-bottom: var(--spacing-lg);
    letter-spacing: -0.01em;
}

/* divider */
.divider {
    height: 1px;
    background: linear-gradient(to right, transparent, var(--color-border), transparent);
    margin: var(--spacing-xl) 0;
}

.control-panel {
    position: relative;
}

.date-control {
    margin-bottom: var(--spacing-lg);
}

.date-control:last-of-type {
    margin-bottom: 0;
}

.control-label {
    display: block;
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-sm);
    text-transform: uppercase;
    letter-spacing: 0.1em;
}

.date-nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: var(--spacing-md);
}

.nav-btn {
    background: var(--color-background);
    color: var(--color-primary);
    border: 1px solid var(--color-border);
    width: 44px;
    height: 44px;
    border-radius: var(--radius-md);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition-fast);
    flex-shrink: 0;
    box-shadow: var(--shadow-sm);
}

.nav-btn:hover {
    background: var(--color-accent);
    color: var(--color-background);
    border-color: var(--color-accent);
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

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

.date-display {
    font-family: var(--font-display);
    font-size: 1.75rem;
    font-weight: 600;
    color: var(--color-primary);
    min-width: 80px;
    text-align: center;
    letter-spacing: 0.02em;
}

.action-section {
    margin-top: var(--spacing-xl);
}

.action-section .btn {
    width: 100%;
    margin-bottom: var(--spacing-sm);
}

.action-section .btn:last-of-type {
    margin-bottom: 0;
}

.btn {
    padding: 0.875rem var(--spacing-lg);
    border: none;
    border-radius: var(--radius-md);
    font-family: var(--font-body);
    font-weight: 600;
    font-size: 0.875rem;
    cursor: pointer;
    transition: var(--transition-base);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    position: relative;
    overflow: hidden;
    box-shadow: var(--shadow-sm);
}

.btn::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.1);
    transform: translate(-50%, -50%);
    transition: width 0.6s, height 0.6s;
}

.btn:hover::before {
    width: 300px;
    height: 300px;
}

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none !important;
}

.btn:disabled::before {
    display: none;
}

.btn-text {
    position: relative;
    z-index: 1;
}

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

.btn-primary:hover:not(:disabled) {
    background: var(--color-accent-dark);
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

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

.btn-secondary:hover:not(:disabled) {
    background: #059669;
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.btn-outline {
    background: transparent;
    color: var(--color-primary);
    border: 1.5px solid var(--color-border);
    box-shadow: none;
}

.btn-outline:hover:not(:disabled) {
    background: var(--color-accent);
    color: var(--color-background);
    border-color: var(--color-accent);
    transform: translateY(-2px);
    box-shadow: var(--shadow-sm);
}

.message {
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    margin-top: var(--spacing-lg);
    font-size: 0.875rem;
    font-weight: 500;
    display: none;
    border-left: 4px solid;
    animation: slideInRight 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

.message.show {
    display: block;
}

.message.success {
    background: var(--color-success-bg);
    color: var(--color-success);
    border-color: var(--color-success);
}

.message.error {
    background: var(--color-error-bg);
    color: var(--color-error);
    border-color: var(--color-error);
}

.message.info {
    background: var(--color-info-bg);
    color: var(--color-info);
    border-color: var(--color-info);
}

.board-wrapper {
    display: flex;
    justify-content: center;
    align-items: flex-start;
    /* ensure board never overflows its column */
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
}

.board {
    display: inline-grid;
    grid-template-columns: repeat(7, var(--cell-size));
    gap: 4px;
    background: transparent;
    padding: var(--spacing-lg);
    border-radius: var(--radius-lg);
    /* prevents shrinking below minimum usable size */
    flex-shrink: 0;
}

/* reduce gap on small screens */
@media (max-width: 600px) {
    .board {
        gap: 3px;
        padding: var(--spacing-sm);
    }
}

@media (max-width: 420px) {
    .board {
        gap: 2px;
        padding: var(--spacing-xs);
    }
}

.cell {
    width: var(--cell-size);
    height: var(--cell-size);
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: var(--radius-sm);
    font-weight: 700;
    font-size: clamp(0.55rem, 1.2vw, 0.8rem);
    letter-spacing: 0.02em;
    transition: var(--transition-fast);
    position: relative;
    overflow: hidden;
}

.cell.blocked {
    background: transparent;
    border: none;
}

.cell.empty {
    background: #f9fafb;
    border: 1px solid rgba(0, 0, 0, 0.1);
}

.cell.label {
    background: #e5e7eb;
    color: #4b5563;
    border: 1px solid rgba(0, 0, 0, 0.1);
    font-weight: 600;
}

.cell.target {
    background: var(--color-primary);
    color: white;
    box-shadow: inset 0 2px 4px rgba(0, 0, 0, 0.3);
    font-weight: 700;
    border: 1px solid rgba(0, 0, 0, 0.1);
}

.cell.piece {
    box-shadow: 
        inset 0 1px 0 rgba(255, 255, 255, 0.3),
        inset 0 -1px 0 rgba(0, 0, 0, 0.1),
        var(--shadow-sm);
    border: 1px solid rgba(0, 0, 0, 0.1);
    animation: pieceAppear 0.4s cubic-bezier(0.34, 1.56, 0.64, 1);
}

.info-panel {
    position: relative;
}

.info-list {
    list-style: none;
    counter-reset: info-counter;
    margin-bottom: var(--spacing-xl);
}

.info-list li {
    counter-increment: info-counter;
    font-size: 0.875rem;
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-sm);
    padding-left: var(--spacing-lg);
    position: relative;
    line-height: 1.6;
}

.info-list li::before {
    content: counter(info-counter);
    position: absolute;
    left: 0;
    top: 0;
    width: 20px;
    height: 20px;
    background: var(--color-accent);
    color: var(--color-background);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.7rem;
    font-weight: 700;
}

.legend {
    margin-top: var(--spacing-xl);
}

.legend-title {
    font-family: var(--font-body);
    font-size: 0.75rem;
    font-weight: 700;
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-md);
    text-transform: uppercase;
    letter-spacing: 0.1em;
}

.legend-item {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-sm);
    font-size: 0.875rem;
    color: var(--color-text-secondary);
}

.legend-cell {
    width: 32px;
    height: 32px;
    border-radius: var(--radius-sm);
    flex-shrink: 0;
}

.legend-cell.target-cell {
    background: var(--color-primary);
    border: 1px solid rgba(0, 0, 0, 0.1);
}

.legend-cell.piece-cell {
    background: #FF9999;
    box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.3);
}

.legend-cell.empty-cell {
    background: #f9fafb;
    border: 2px solid white;
}

.spinner {
    border: 3px solid rgba(255, 255, 255, 0.3);
    border-top: 3px solid white;
    border-radius: 50%;
    width: 18px;
    height: 18px;
    animation: spin 0.8s linear infinite;
    display: inline-block;
    margin-right: var(--spacing-sm);
    vertical-align: middle;
}


@keyframes fadeIn {
    from { opacity: 0; transform: translateY(20px); }
    to   { opacity: 1; transform: translateY(0); }
}

@keyframes fadeInDown {
    from { opacity: 0; transform: translateY(-30px); }
    to   { opacity: 1; transform: translateY(0); }
}

@keyframes slideInRight {
    from { opacity: 0; transform: translateX(-20px); }
    to   { opacity: 1; transform: translateX(0); }
}

@keyframes pieceAppear {
    from { opacity: 0; transform: scale(0.8); }
    to   { opacity: 1; transform: scale(1); }
}

@keyframes spin {
    0%   { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* smooth scrolling */
html {
    scroll-behavior: smooth;
}

/* focus styles for accessibility */
button:focus-visible,
.nav-btn:focus-visible {
    outline: 2px solid var(--color-accent);
    outline-offset: 2px;
}