:root {
    /* Typographic Families */
    --font-heading: 'Lora', 'Cambria', 'Georgia', serif;
    --font-body: 'Aptos', system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
    --font-mono: 'JetBrains Mono', monospace;

    /* Light Theme Custom Properties (Default) */
    --bg-base: #f8fafc;
    --bg-surface: #ffffff;
    --bg-surface-hover: #f1f5f9;
    --border-color: #e2e8f0;
    --border-hover: #cbd5e1;
    
    --text-primary: #0f172a;
    --text-secondary: #475569;
    --text-muted: #64748b;
    
    --accent: #1e3a8a;         /* Deep Navy */
    --accent-hover: #1e40af;
    --accent-soft: #eff6ff;
    
    /* Expedition Muted Color Codes for Light Mode */
    --exp-yellow: #b45309;
    --exp-blue: #1d4ed8;
    --exp-white: #475569;
    --exp-green: #047857;
    --exp-red: #b91c1c;

    --card-gradient-yellow: linear-gradient(135deg, #fef3c7 0%, #fde68a 100%);
    --card-gradient-blue: linear-gradient(135deg, #dbeafe 0%, #bfdbfe 100%);
    --card-gradient-white: linear-gradient(135deg, #f1f5f9 0%, #e2e8f0 100%);
    --card-gradient-green: linear-gradient(135deg, #d1fae5 0%, #a7f3d0 100%);
    --card-gradient-red: linear-gradient(135deg, #fee2e2 0%, #fecaca 100%);
    
    --shadow-sm: 0 1px 3px rgba(15, 23, 42, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(15, 23, 42, 0.05), 0 2px 4px -1px rgba(15, 23, 42, 0.03);
    
    --transition: 0.15s cubic-bezier(0.4, 0, 0.2, 1);
}

/* Dark Theme applied via media query */
@media (prefers-color-scheme: dark) {
    :root:not(.theme-light) {
        --bg-base: #0b0f19;
        --bg-surface: #111827;
        --bg-surface-hover: #1f2937;
        --border-color: #1f2937;
        --border-hover: #374151;
        
        --text-primary: #f1f5f9;
        --text-secondary: #cbd5e1;
        --text-muted: #94a3b8;
        
        --accent: #60a5fa;
        --accent-hover: #93c5fd;
        --accent-soft: #1e3a8a;
        
        /* Expedition Sophisticated Codes for Dark Mode */
        --exp-yellow: #f59e0b;
        --exp-blue: #60a5fa;
        --exp-white: #e2e8f0;
        --exp-green: #34d399;
        --exp-red: #f87171;

        --card-gradient-yellow: linear-gradient(135deg, #451a03 0%, #78350f 100%);
        --card-gradient-blue: linear-gradient(135deg, #172554 0%, #1e3b8a 100%);
        --card-gradient-white: linear-gradient(135deg, #0f172a 0%, #334155 100%);
        --card-gradient-green: linear-gradient(135deg, #022c22 0%, #064e3b 100%);
        --card-gradient-red: linear-gradient(135deg, #450a0a 0%, #7f1d1d 100%);
        
        --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.3);
        --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.3), 0 2px 4px -1px rgba(0, 0, 0, 0.2);
    }
}

/* Explicit Dark Theme overrides */
:root.theme-dark {
    --bg-base: #0b0f19;
    --bg-surface: #111827;
    --bg-surface-hover: #1f2937;
    --border-color: #1f2937;
    --border-hover: #374151;
    
    --text-primary: #f1f5f9;
    --text-secondary: #cbd5e1;
    --text-muted: #94a3b8;
    
    --accent: #60a5fa;
    --accent-hover: #93c5fd;
    --accent-soft: #1e3a8a;
    
    --exp-yellow: #f59e0b;
    --exp-blue: #60a5fa;
    --exp-white: #e2e8f0;
    --exp-green: #34d399;
    --exp-red: #f87171;

    --card-gradient-yellow: linear-gradient(135deg, #451a03 0%, #78350f 100%);
    --card-gradient-blue: linear-gradient(135deg, #172554 0%, #1e3b8a 100%);
    --card-gradient-white: linear-gradient(135deg, #0f172a 0%, #334155 100%);
    --card-gradient-green: linear-gradient(135deg, #022c22 0%, #064e3b 100%);
    --card-gradient-red: linear-gradient(135deg, #450a0a 0%, #7f1d1d 100%);
    
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.3), 0 2px 4px -1px rgba(0, 0, 0, 0.2);
}

/* Explicit Light Theme overrides */
:root.theme-light {
    --bg-base: #f8fafc;
    --bg-surface: #ffffff;
    --bg-surface-hover: #f1f5f9;
    --border-color: #e2e8f0;
    --border-hover: #cbd5e1;
    
    --text-primary: #0f172a;
    --text-secondary: #475569;
    --text-muted: #64748b;
    
    --accent: #1e3a8a;
    --accent-hover: #1e40af;
    --accent-soft: #eff6ff;
    
    --exp-yellow: #b45309;
    --exp-blue: #1d4ed8;
    --exp-white: #475569;
    --exp-green: #047857;
    --exp-red: #b91c1c;

    --card-gradient-yellow: linear-gradient(135deg, #fef3c7 0%, #fde68a 100%);
    --card-gradient-blue: linear-gradient(135deg, #dbeafe 0%, #bfdbfe 100%);
    --card-gradient-white: linear-gradient(135deg, #f1f5f9 0%, #e2e8f0 100%);
    --card-gradient-green: linear-gradient(135deg, #d1fae5 0%, #a7f3d0 100%);
    --card-gradient-red: linear-gradient(135deg, #fee2e2 0%, #fecaca 100%);
    
    --shadow-sm: 0 1px 3px rgba(15, 23, 42, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(15, 23, 42, 0.05), 0 2px 4px -1px rgba(15, 23, 42, 0.03);
}

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

body {
    font-family: var(--font-body);
    background-color: var(--bg-base);
    color: var(--text-primary);
    min-height: 100vh;
    line-height: 1.6;
    display: flex;
    flex-direction: column;
    transition: background-color var(--transition), color var(--transition);
    -webkit-font-smoothing: antialiased;
}

.container {
    max-width: 1250px;
    width: 100%;
    margin: 0 auto;
    padding: 0 2rem;
}

/* Skip Link */
.skip-link {
    position: absolute;
    top: -100px;
    left: 50%;
    transform: translateX(-50%);
    background: var(--accent);
    color: #ffffff;
    padding: 0.5rem 1rem;
    border-radius: 4px;
    z-index: 100;
    transition: top var(--transition);
    font-weight: 500;
    text-decoration: none;
    font-size: 0.875rem;
}

.skip-link:focus {
    top: 15px;
    outline: 2px solid var(--accent);
}

/* Top Navigation Bar */
.top-bar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1.5rem 0;
    margin-bottom: -1rem;
}

.back-home-link {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    text-decoration: none;
    color: var(--text-secondary);
    font-size: 0.875rem;
    font-weight: 600;
    transition: all var(--transition);
}

.back-home-link:hover {
    color: var(--text-primary);
}

.back-home-link svg {
    width: 16px;
    height: 16px;
    transition: transform var(--transition);
}

.back-home-link:hover svg {
    transform: translateX(-3px);
}

.theme-toggle-btn {
    background: transparent;
    border: 1px solid var(--border-color);
    padding: 0.5rem;
    border-radius: 8px;
    color: var(--text-secondary);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all var(--transition);
}

.theme-toggle-btn:hover {
    border-color: var(--border-hover);
    color: var(--text-primary);
    background: var(--bg-surface-hover);
}

.theme-toggle-btn svg {
    width: 20px;
    height: 20px;
}

.sun-icon { display: block; }
.moon-icon { display: none; }

:root.theme-dark .sun-icon { display: none; }
:root.theme-dark .moon-icon { display: block; }

@media (prefers-color-scheme: dark) {
    :root:not(.theme-light) .sun-icon { display: none; }
    :root:not(.theme-light) .moon-icon { display: block; }
}

/* Header */
header {
    padding: 2.5rem 0 2rem;
    text-align: center;
    border-bottom: 1px solid var(--border-color);
}

.header-accent {
    font-family: var(--font-body);
    font-size: 0.75rem;
    font-weight: 600;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    color: var(--text-muted);
    margin-bottom: 0.5rem;
    display: inline-block;
}

.logo {
    font-family: var(--font-heading);
    font-size: 2.75rem;
    font-weight: 400;
    line-height: 1.1;
    color: var(--text-primary);
    margin-bottom: 0.5rem;
    letter-spacing: -0.01em;
}

.logo span {
    color: var(--accent);
    font-weight: 700;
}

.tagline {
    font-size: 1.05rem;
    color: var(--text-secondary);
}

/* App structure layout container */
.app-container {
    flex: 1;
    max-width: 1250px;
    width: 100%;
    margin: 0 auto;
    padding: 2.5rem 2rem 5rem;
}

main {
    padding-top: 3.5rem;
    padding-bottom: 3.5rem;
}

/* Board layout split grid */
.game-board-layout {
    display: grid;
    grid-template-columns: 1.6fr 1fr;
    gap: 2.5rem;
}

.board-area {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
    background: var(--bg-surface);
    border-radius: 8px;
    border: 1px solid var(--border-color);
    padding: 1.5rem;
    box-shadow: var(--shadow-sm);
}

.sidebar-area {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

/* Card element stylings */
.card {
    background: var(--bg-surface);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 1.5rem;
    box-shadow: var(--shadow-sm);
}

.card h3, .expeditions-row h3, .discard-piles-wrapper h3 {
    font-family: var(--font-heading);
    font-size: 1.05rem;
    font-weight: 400;
    color: var(--text-primary);
    margin-bottom: 0.8rem;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 0.35rem;
}

/* Expeditions lines rows styling */
.expeditions-row {
    background: var(--bg-base);
    padding: 1.25rem;
    border-radius: 6px;
    border: 1px solid var(--border-color);
}

.colors-grid, .discard-grid {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 10px;
}

/* Visual Column Piles */
.col-pile {
    min-height: 110px;
    background: var(--bg-surface);
    border-radius: 6px;
    border: 1px dashed var(--border-color);
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 6px;
    gap: 6px;
    position: relative;
}

.colors-grid .col-pile {
    min-height: 170px;
    padding-bottom: 20px;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0;
}

/* Stacked solitaire card overlap */
.colors-grid .col-pile .game-card {
    margin-top: -72px;
    position: relative;
    z-index: 1;
    box-shadow: 0 -2px 6px rgba(0, 0, 0, 0.1);
}

.colors-grid .col-pile .game-card:first-child {
    margin-top: 0;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.08);
}

.colors-grid .col-pile .game-card:hover {
    transform: translateY(-8px);
    z-index: 100;
    box-shadow: var(--shadow-md);
}

.empty-slot-placeholder {
    color: var(--text-muted);
    font-size: 1.5rem;
    font-weight: 700;
    opacity: 0.25;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

/* Central Discards Board */
.central-board {
    display: grid;
    grid-template-columns: 1fr 3fr;
    gap: 1.5rem;
    align-items: center;
    background: var(--bg-base);
    padding: 1.25rem;
    border-radius: 6px;
    border: 1px solid var(--border-color);
}

.draw-pile-container {
    display: flex;
    justify-content: center;
}

.card-back {
    width: 76px;
    height: 108px;
    border-radius: 6px;
    background: var(--accent);
    border: 1px solid var(--accent);
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    gap: 6px;
    position: relative;
    box-shadow: var(--shadow-sm);
}

.card-back.draw-deck {
    box-shadow: var(--shadow-md);
    cursor: pointer;
}

.card-title {
    font-size: 0.7rem;
    font-weight: 600;
    letter-spacing: 0.1em;
    color: rgba(255,255,255,0.7);
}

.deck-count {
    font-size: 1.5rem;
    font-weight: 700;
    color: #ffffff;
}

/* Game Expeditions Cards Visual Grid */
.game-card {
    width: 76px;
    height: 108px;
    border-radius: 6px;
    border: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    padding: 6px;
    cursor: pointer;
    position: relative;
    transition: all var(--transition);
    box-shadow: var(--shadow-sm);
}

.game-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
}

.game-card.selected {
    border-color: var(--accent) !important;
    box-shadow: 0 0 10px var(--accent) !important;
    transform: translateY(-6px);
}

/* Academic Styled Card Themes mapping custom variables */
.game-card.yellow {
    background: var(--card-gradient-yellow);
    color: var(--exp-yellow);
    border-color: rgba(180, 83, 9, 0.25);
}
.game-card.blue {
    background: var(--card-gradient-blue);
    color: var(--exp-blue);
    border-color: rgba(29, 78, 216, 0.25);
}
.game-card.white {
    background: var(--card-gradient-white);
    color: var(--exp-white);
    border-color: rgba(71, 85, 105, 0.25);
}
.game-card.green {
    background: var(--card-gradient-green);
    color: var(--exp-green);
    border-color: rgba(4, 120, 87, 0.25);
}
.game-card.red {
    background: var(--card-gradient-red);
    color: var(--exp-red);
    border-color: rgba(185, 28, 28, 0.25);
}

.card-corner {
    font-size: 0.75rem;
    font-weight: 700;
}
.card-center {
    font-size: 1.1rem;
    font-weight: 700;
    text-align: center;
    align-self: center;
}

/* Sidebar controls card */
.control-card {
    border-left: 4px solid var(--accent);
}

.action-box {
    display: flex;
    flex-direction: column;
    gap: 1.25rem;
}

.pulse-indicator {
    width: 8px;
    height: 8px;
    background-color: var(--accent);
    border-radius: 50%;
    animation: pulse 1.8s infinite ease-in-out;
    align-self: flex-start;
}

#action-instruction {
    font-size: 0.95rem;
    font-weight: 600;
    color: var(--text-primary);
    line-height: 1.45;
}

.choice-buttons {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
}

/* Hand Section */
.hand-grid {
    display: flex;
    gap: 8px;
    overflow-x: auto;
    padding: 8px 0;
    min-height: 125px;
}

.hand-grid::-webkit-scrollbar {
    height: 5px;
}
.hand-grid::-webkit-scrollbar-thumb {
    background: var(--border-color);
    border-radius: 4px;
}

/* Restrained standard buttons */
.btn {
    padding: 0.55rem 1.25rem;
    border-radius: 4px;
    font-size: 0.85rem;
    font-weight: 600;
    font-family: var(--font-body);
    cursor: pointer;
    transition: all var(--transition);
    border: 1px solid transparent;
}

.btn-primary {
    background: var(--accent);
    color: #ffffff;
}
.btn-primary:hover {
    background: var(--accent-hover);
    transform: translateY(-1px);
}

.btn-secondary {
    background: transparent;
    color: var(--text-secondary);
    border-color: var(--border-color);
}
.btn-secondary:hover {
    background: var(--bg-surface-hover);
    color: var(--text-primary);
    border-color: var(--border-hover);
}

.btn-color-yellow { border-color: var(--exp-yellow); color: var(--exp-yellow); }
.btn-color-blue { border-color: var(--exp-blue); color: var(--exp-blue); }
.btn-color-white { border-color: var(--exp-white); color: var(--exp-white); }
.btn-color-green { border-color: var(--exp-green); color: var(--exp-green); }
.btn-color-red { border-color: var(--exp-red); color: var(--exp-red); }

/* Draw Pile choice divider inside action boxes */
.draw-divider {
    width: 100%;
    display: flex;
    align-items: center;
    gap: 8px;
    margin: 4px 0;
    color: var(--text-muted);
    font-size: 0.725rem;
    letter-spacing: 0.04em;
    text-transform: uppercase;
}
.draw-divider::before,
.draw-divider::after {
    content: '';
    flex: 1;
    height: 1px;
    background: var(--border-color);
}

.discard-top-hint {
    font-size: 0.7rem;
    font-weight: 400;
    opacity: 0.75;
    margin-left: 2px;
}

/* System Engine CLI Logs */
.terminal-card pre {
    background: var(--bg-base);
    padding: 1rem;
    border-radius: 6px;
    height: 160px;
    overflow-y: auto;
    font-family: var(--font-mono);
    font-size: 0.78rem;
    line-height: 1.45;
    color: var(--text-primary);
    border: 1px solid var(--border-color);
}

/* Modals Overlay definitions */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    background: rgba(15, 23, 42, 0.4);
    backdrop-filter: blur(4px);
    -webkit-backdrop-filter: blur(4px);
    z-index: 10;
    display: flex;
    justify-content: center;
    align-items: center;
}

.modal-card {
    background: var(--bg-surface);
    border: 1px solid var(--border-color);
    padding: 2.5rem;
    border-radius: 8px;
    text-align: center;
    box-shadow: var(--shadow-md);
    max-width: 440px;
    width: 90%;
}

.modal-card h2 {
    font-family: var(--font-heading);
    font-size: 1.8rem;
    font-weight: 400;
    margin-bottom: 0.5rem;
    color: var(--text-primary);
}

.winner-announcement {
    color: var(--text-secondary);
    font-size: 1rem;
    margin-bottom: 1.5rem;
    font-weight: 600;
}

/* State controls */
.hidden { display: none !important; }

@keyframes pulse {
    0% { transform: scale(0.92); opacity: 0.4; }
    50% { transform: scale(1.08); opacity: 1; }
    100% { transform: scale(0.92); opacity: 0.4; }
}

@media (max-width: 992px) {
    .game-board-layout {
        grid-template-columns: 1fr;
        gap: 2rem;
    }
    .app-container {
        padding: 1.5rem 1rem 3rem;
    }
}

.inactive-hand {
    opacity: 0.55;
    pointer-events: none;
    filter: grayscale(20%);
    transition: all var(--transition);
}
.inactive-hand .game-card {
    cursor: not-allowed !important;
}

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