:root {
	--cell-w-h: 70px;
	--cell-font-size: 40px;
	--corner-borders: 2px solid #000000;
	--gap: 1px;
	--board-padding: 12px;
	--boarders-focus: 4px solid #007bff;
	--select-width: 100%;
	--select-font-size: 14px;
	--select-pad-x: 14px;
	--select-pad-y: 10px;
	--select-radius: 8px;
	--select-bg: #ffffff;
	--select-color: #111827;
	--select-border: 1px solid #d1d5db;
	--select-focus-color: #3b82f6;
	--select-arrow-color: #ff0000;
	--select-arrow-size: 24px;
}
body {
	font-family: Arial, sans-serif;
	background: #f4f4f4;
	display: flex;
	justify-content: center;
	align-items: flex-start;
	padding-top: 40px;
}
#sudoku-wrapper {
	background: #fff;
	padding: 20px 25px 25px;
	border-radius: 8px;
	box-shadow: 0 0 10px rgba(0,0,0,0.15);
}
#sudoku-wrapper h1 {
	margin-top: 0;
	text-align: center;
}
#btn-new {
	display: block;
	margin: 10px auto;
	padding: 8px 16px;
	border: none;
	background: #007bff;
	color: #fff;
	border-radius: 4px;
	cursor: pointer;
	font-size: 14px;
}
#btn-new:hover {
	background: #0056b3;
}
#btn-solve {
	display: block;
	margin: 10px auto;
	padding: 8px 16px;
	background: #28a745;
	color: #fff;
	border: none;
	border-radius: 4px;
	cursor: pointer;
}
#btn-solve:hover {
	background: #1e7e34;
}
#btn-check {
	display: block;
	margin: 10px auto;
	padding: 8px 16px;
	background: #4144e9;
	color: #ffffff;
	border: none;
	border-radius: 4px;
	cursor: pointer;
}
#btn-check:hover {
	background: #261e7e;
}
#btn-close {
	display: block;
	margin: 10px auto;
	padding: 8px 16px;
	background: #e94141;
	color: #ffffff;
	border: none;
	border-radius: 4px;
	cursor: pointer;
}
#btn-close:hover {
	background: #7e1e1e;
}
#sudoku-board {
	display: grid;
	padding: var(--board-padding);
	grid-template-columns: repeat(9, var(--cell-w-h));
	grid-template-rows: repeat(9, var(--cell-w-h));
	gap: var(--gap);
	border: 2px solid #000;
}
.sudoku-cell {
	width: var(--cell-w-h);
	height: var(--cell-w-h);
	box-sizing: border-box;
	border: 1px solid #ccc;
	text-align: center;
	font-size: 18px;
	line-height: var(--cell-w-h);
	background: #fafafa;
}
.sudoku-cell input {
	width: calc(var(--cell-w-h) - 8px);
	height: calc(var(--cell-w-h) - 8px);
	border: none;
	text-align: center;
	font-size: var(--cell-font-size);
	background: transparent;
}
.sudoku-cell input:focus {
	outline: var(--boarders-focus);
}
/* Bold borders for 3x3 blocks */
.sudoku-cell.block-right {
	border-right: var(--corner-borders);
}
.sudoku-cell.block-bottom {
	border-bottom: var(--corner-borders);
}
.sudoku-cell.block-left {
	border-left: var(--corner-borders);
}
.sudoku-cell.block-top {
	border-top: var(--corner-borders);
}
.sudoku-cell.block-top-big {
	border-top: 4px solid black
}
.sudoku-cell input.error {
	background: #ffcccc;
	color: #900;
	font-weight: bold;
}
#check-result {
	margin-top: 15px;
	font-size: 18px;
	font-weight: bold;
	text-align: center;
}
#check-result.success {
	color: green;
}
#check-result.error {
	color: red;
}
#difficulty {
	margin-left: 10px;
	padding: 5px;
	font-size: 14px;
}
.select-wrapper {
	position: relative;
	display: flex;
	width: var(--select-width);
}
.custom-select {
	width: 100%;
	font-family: inherit;
	font-size: var(--select-font-size);
	padding: var(--select-pad-y) 45px var(--select-pad-y) var(--select-pad-x);
	border-radius: var(--select-radius);
	background: var(--select-bg);
	color: var(--select-color);
	border: var(--select-border);
	-webkit-appearance: none;
	-moz-appearance: none;
	appearance: none;
	outline: none;
	cursor: pointer;
	transition: border-color 0.2s ease, box-shadow 0.2s ease;
}
.custom-select:focus {
	border-color: var(--select-focus-color);
	box-shadow: 0 0 0 2px rgba(59,130,246,0.35);
}
.select-arrow {
	position: absolute;
	right: 14px;
	top: 50%;
	transform: translateY(-50%);
	pointer-events: none;
	width: var(--select-arrow-size);
	height: var(--select-arrow-size);
}
.sudoku-cell {
	position: relative;
}