:root {
    --primary-color: #6366f1;
    --primary-hover: #4f46e5;
    --bg-color: #0f172a;
    --surface-color: #1e293b;
    --text-color: #f8fafc;
    --text-muted: #94a3b8;
    --accent-color: #22d3ee;
    --board-size: 400px;
    --gap-size: 4px;
    --tile-size: calc((var(--board-size) - (var(--gap-size) * 2)) / 3);
    --transition-speed: 0.3s;
}

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

body {
    font-family: 'Outfit', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    overflow: hidden;
}

.app-container {
    text-align: center;
    max-width: 500px;
    width: 100%;
    padding: 2rem;
}

header {
    margin-bottom: 2rem;
}

h1 {
    font-size: 2.5rem;
    font-weight: 700;
    background: linear-gradient(135deg, var(--primary-color), var(--accent-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    margin-bottom: 0.5rem;
}

p {
    color: var(--text-muted);
    font-weight: 300;
}

.game-container {
    position: relative;
    width: var(--board-size);
    height: var(--board-size);
    margin: 0 auto 2rem;
    background-color: var(--surface-color);
    border-radius: 1rem;
    padding: var(--gap-size);
    box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
}

.puzzle-board {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-template-rows: repeat(3, 1fr);
    gap: var(--gap-size);
    width: 100%;
    height: 100%;
}

.tile {
    background-image: url('puzzle_image.png'); /* Will be set dynamically if needed, but hardcoded for now as per plan */
    background-size: var(--board-size) var(--board-size); /* Ensure image covers the whole board logic */
    border-radius: 0.5rem;
    cursor: pointer;
    transition: transform var(--transition-speed) ease, opacity 0.2s;
    position: relative;
}

.tile:hover {
    opacity: 0.9;
    transform: scale(0.98);
}

.tile.empty {
    background: transparent;
    cursor: default;
    pointer-events: none;
}

/* Success Overlay */
.success-overlay {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(15, 23, 42, 0.85);
    backdrop-filter: blur(4px);
    display: flex;
    justify-content: center;
    align-items: center;
    border-radius: 1rem;
    opacity: 1;
    transition: opacity 0.5s ease;
    z-index: 10;
}

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

.success-content {
    transform: translateY(0);
    transition: transform 0.5s ease;
}

.success-overlay.hidden .success-content {
    transform: translateY(20px);
}

.success-content h2 {
    font-size: 2rem;
    color: var(--accent-color);
    margin-bottom: 0.5rem;
}

/* Controls */
.controls {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 1rem;
}

.stats {
    font-size: 1.1rem;
    color: var(--text-color);
    background: var(--surface-color);
    padding: 0.5rem 1rem;
    border-radius: 0.5rem;
}

button {
    font-family: inherit;
    font-weight: 500;
    font-size: 1rem;
    padding: 0.75rem 1.5rem;
    border: none;
    border-radius: 0.5rem;
    cursor: pointer;
    transition: all 0.2s;
}

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

.btn-primary:hover {
    background-color: var(--primary-hover);
    transform: translateY(-2px);
    box-shadow: 0 4px 6px -1px rgba(99, 102, 241, 0.4);
}

.btn-secondary {
    background-color: var(--surface-color);
    color: var(--text-color);
    border: 1px solid rgba(255, 255, 255, 0.1);
}

.btn-secondary:hover {
    background-color: rgba(255, 255, 255, 0.1);
}

@media (max-width: 450px) {
    :root {
        --board-size: 320px;
    }
}