style.css

:root {
	--main: #3D1766;
	--second: #6F1AB6;
	--third: #FF0032;
	--contrast: #CD0404;
}

body {
	overflow: hidden;
	width: 100vw;
	height: 100vh;
	margin: unset;
	background-image: linear-gradient(to bottom, var(--main) 0%, var(--contrast) 100%);
	padding-top: 7.5vmax;
	padding-bottom: 0;
	display: grid;
	justify-items: center;
	align-items: baseline;
}

h1 {
	font-size: 4em;
	color: var(--contrast);
}

form {
	display: flex;
	flex-direction: column;
	place-content: center;
	align-items: center;
	row-gap: 5em;
}

input[type="number"] {
	transition-property: border-color;
	transition-duration: 500ms;
	background-color: transparent;
	color: var(--third);
	outline-style: none;
	border-width: 0 0 .25em 0;
	border-style: solid;
	border-color: var(--contrast);
	border-radius: .15em;
	font-size: 4em;
	text-align: center;
	caret-color: var(--contrast);
}

input[type="number"]::-webkit-inner-spin-button,
input[type="number"]::-webkit-outer-spin-button {
	appearance: none;
	margin: 0;
}

input[type="number"]:hover,
input[type="number"]:focus {
	border-color: var(--third);
}

input[type="submit"] {
	transition-property: scale, border-color;
	transition-duration: 500ms;
	scale: 1;
	background-color: transparent;
	color: var(--second);
	outline-style: none;
	border-color: var(--main);
	border-style: solid;
	border-radius: 1em;
	border-width: .25em;
	font-size: 2.5em;
	font-weight: bold;
	padding: .25em .75em;
}

input[type="submit"]:hover {
	scale: 1.2;
	border-color: var(--second);
}

input[type="submit"]:active {
	scale: .8;
	border-color: var(--second);
}