style.css

:root{
	--foreground-color: hsl(0, 50%, 50%);
	--background-color: hsl(0, 0%, 0%);
}

@media (max-width: 600px) {
	html {
		font-size: 1.5rem; 
	}
}

@media (min-width: 601px) {
	html {
		font-size: 1rem; 
	}
}

body {
	color: var(--foreground-color);
	background-color: var(--background-color);
}

hr {
	border-color: var(--foreground-color);
}

nav {
	color: var(--foreground-color);
	text-align: center;
	clear: both;
}

.board {
	display: grid;
	grid-template-columns: repeat(3, 1fr);
	grid-template-rows: repeat(3, 1fr);
	max-width: 12rem; 
	max-height: 12rem; 
}

.square {
	border: 0.01rem solid var(--foreground-color);
	height: 4rem;
	width: 4rem;
	font-size: 3rem;
	display: flex;
	align-items: center;
	justify-content: center;
}

.square:nth-child(3n+1) {
	border-left: 0;
}

.square:nth-child(3n+3) {
	border-right: 0;
}

.square:nth-child(-n+3) {
	border-top: 0;
}

.square:nth-child(n+7) {
	border-bottom: 0;
}