styles.css

html {
	box-sizing: border-box;
	font-size: 16px;
	font-size: 25pt;
}

*,
*::before,
*::after {
	box-sizing: inherit;
}

body {
	margin: 0;
	display: flex;
	min-height: 100vh;
	color: #303f46;
	font-family: "Nunito Sans", sans-serif;
}

#root {
	margin: auto;
	width: 15em;
	min-height: 5em;
	text-align: center;
}

.quantity-picker {
	display: flex;
	justify-content: center;
	align-items: center;
	max-width: 5em;
	margin: 0 auto;
}

.quantity-picker > div {
	display: flex;
	justify-content: center;
	align-items: center;
}

.input-container {
	flex: 1;
	margin: 0 0.5rem;
}

.input-container input {
	width: 100%;
	text-align: center;
	font-size: 1rem;
	border: 1px solid #ddd;
	border-radius: 2px;
}

.icon-button {
	--size: 1rem;
	all: unset;
	position: relative;
	line-height: 1;
	margin: 0;
	background-color: rgb(0, 157, 255);
	color: #fff;
	width: var(--size);
	height: var(--size);
	border-radius: calc(var(--size) / 2);
	display: flex;
	align-items: center;
	justify-content: center;
	user-select: none;
}

.icon-button > span {
	vertical-align: initial;
}

.icon-button:focus {
	outline: none;
}

.icon-button:focus::before {
	--s: var(--size);
	--size1: calc(var(--s) + (var(--offset) * 2));
	--offset: 2px;
	--thickness: 3px;
	content: "";
	position: absolute;
	width: var(--size1);
	height: var(--size1);
	border: var(--thickness) solid rgba(0, 157, 255, 0.6);
	border-radius: calc((var(--size1) + var(--thickness) * 2) / 2);
}

.quantity-picker-error {
	color: crimson;
}