style.css

:root {
	--bg-color: #f5f5f5;
	--fg-color: #000000e0;
}

@media (prefers-color-scheme: dark) {
	:root {
		--bg-color: #1d1e20;
		--fg-color: #ffffffd6;
	}
}

body {
	margin: 0;
	background-color: var(--bg-color);
	color: var(--fg-color);
	font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
}

header {
	width: 100%;
	min-height: 4em;
	padding: 1em;
	box-sizing: border-box;

	position: sticky;
	top: 0;
	left: 0;
	z-index: 10;

	background-color: var(--bg-color);
	box-shadow: 0 0px 8px 0px darkgray;

	display: flex;
	flex-flow: row nowrap;
	justify-content: space-between;
	align-items: center;
}

header > form {
	text-align: right;
}

header > h2 {
	margin: 0;
}

header > form label {
	margin-left: 1em;
}

header > form > div {
	display: inline-block;
	margin: 1px;
}

header > form select {
	background-color: var(--bg-color);
	color: var(--fg-color);
	border: 1px solid var(--fg-color);
	padding: 2px;
}

header > form input[type="number"] {
	background-color: var(--bg-color);
	color: var(--fg-color);
	border: 1px solid var(--fg-color);
	padding: 2px 4px;
	box-sizing: border-box;
}

.canvas-container {
	min-width: 600px;
	max-width: 1500px;
	text-align: center;
	padding: 25px;
	position: relative;
	margin: 0 auto;
}

canvas {
	max-width: 100%;
}

#error-msg {
	text-align: center;
	margin-top: 40vh;
}

@media (prefers-color-scheme: dark) {
	header {
		box-shadow: 0 0px 8px 0px #040404;
	}
}