:root {
	--bg: #0f1724;
	--card: #0b1220;
	--tile: #e6ecf2;
	--accent: #4f46e5;
	--gap: 12px;
}
* {
	box-sizing: border-box;
}
html,
body {
	height: 100%;
}
body {
	margin: 0;
	font-family: system-ui, -apple-system, Segoe UI, Roboto, "Helvetica Neue",
		Arial;
	background: linear-gradient(180deg, #071029 0%, #0b1220 100%);
	color: var(--tile);
	display: flex;
	align-items: center;
	justify-content: center;
	padding: 24px;
}
header {
	width: 100%;
	max-width: 520px;
	margin-bottom: 18px;
	text-align: center;
}
header h1 {
	margin: 0.25rem 0;
	font-size: 1.6rem;
}
.subtitle {
	margin: 0;
	color: rgba(230, 236, 242, 0.8);
	font-size: 0.9rem;
}
.game {
	background: rgba(255, 255, 255, 0.02);
	padding: 20px;
	border-radius: 12px;
	display: flex;
	flex-direction: column;
	gap: 16px;
	align-items: center;
}
.board {
	display: grid;
	grid-template-columns: repeat(3, 1fr);
	grid-template-rows: repeat(3, 1fr);
	gap: var(--gap);
	width: min(420px, 90vw);
	aspect-ratio: 1/1;
	padding: var(--gap);
	background: linear-gradient(
		180deg,
		rgba(255, 255, 255, 0.02),
		rgba(255, 255, 255, 0.01)
	);
	border-radius: 10px;
	position: relative;
}
.tile {
	background: var(--tile);
	color: #092029;
	display: flex;
	align-items: center;
	justify-content: center;
	font-weight: 700;
	font-size: 1.6rem;
	border-radius: 8px;
	user-select: none;
	box-shadow: 0 6px 18px rgba(2, 6, 23, 0.5);
	transition: transform 200ms cubic-bezier(0.2, 0.8, 0.2, 1), box-shadow 200ms;
}
.tile.blank {
	background: transparent;
	box-shadow: inset 0 0 0 2px var(--accent);
}
.tile.dragging {
	opacity: 0.6;
	transform: scale(0.98);
}
.tile.invalid {
	animation: shake 260ms ease;
}
@keyframes shake {
	0% {
		transform: translateX(0);
	}
	25% {
		transform: translateX(-8px);
	}
	50% {
		transform: translateX(6px);
	}
	75% {
		transform: translateX(-4px);
	}
	100% {
		transform: translateX(0);
	}
}

.controls {
	display: flex;
	gap: 10px;
}
button {
	background: black;
	border: 3px solid var(--accent);
	padding: 8px 12px;
	border-radius: 8px;
	color: var(--tile);
	cursor: pointer;
}
button:active {
	transform: translateY(1px);
}

.overlay {
	position: fixed;
	inset: 0;
	display: flex;
	align-items: center;
	justify-content: center;
	pointer-events: none;
	opacity: 0;
	transition: opacity 320ms;
}
.overlay.visible {
	pointer-events: auto;
	opacity: 1;
	/* visible backdrop to clearly dim the game */
	background: rgba(2, 6, 23, 0.75);
	backdrop-filter: blur(6px);
}
.win-card {
	/* slightly more opaque card so text reads well on the backdrop */
	background: rgba(255, 255, 255, 0.06);
	padding: 28px;
	border-radius: 12px;
	text-align: center;
	box-shadow: 0 10px 40px rgba(3, 8, 23, 0.7);
	transform: translateY(-6px);
	border: 1px solid rgba(255,255,255,0.08);
}
.win-card h2 {
	margin: 0 0 8px 0;
}
.win-actions {
	margin-top: 12px;
}

.board.won {
	outline: 4px solid rgba(79, 70, 229, 0.25);
	box-shadow: 0 8px 40px rgba(79, 70, 229, 0.08);
}
.board.won .tile {
	animation: pop 700ms ease both;
}
@keyframes pop {
	0% {
		transform: translateY(0) scale(1) rotate(0deg);
	}
	30% {
		transform: translateY(-8px) scale(1.02) rotate(-2deg);
	}
	60% {
		transform: translateY(6px) scale(0.99) rotate(2deg);
	}
	100% {
		transform: translateY(0) scale(1) rotate(0deg);
	}
}

/* Responsive adjustments for small screens */
@media (max-width: 600px) {
	body { display: block;  }
}

@media (prefers-reduced-motion: reduce) {
	.tile,
	.board,
	.win-card {
		transition: none;
		animation: none;
	}
}