codepens/lotsa-notifications/dist/style.css

* {
	border: 0;
	box-sizing: border-box;
	margin: 0;
	padding: 0;
}
:root {
	--hue: 223;
	--bg: hsl(var(--hue),10%,90%);
	--fg: hsl(var(--hue),10%,10%);
	--transDur: 0.15s;
	font-size: calc(16px + (24 - 16) * (100vw - 320px) / (1280 - 320));
}
body,
button {
	color: var(--fg);
	font: 1em/1.5 "DM Sans", "Helvetica Neue", Helvetica, sans-serif;
}
body {
	background-color: var(--bg);
	height: 100vh;
	display: grid;
	place-items: center;
	transition: background-color var(--transDur);
}
.notification {
	padding-bottom: 0.75em;
	position: fixed;
	top: 1.5em;
	right: 1.5em;
	width: 18.75em;
	max-width: calc(100% - 3em);
	transition: transform 0.15s ease-out;
	-webkit-user-select: none;
	-moz-user-select: none;
	user-select: none;
}
.notification__box,
.notification__content,
.notification__btns {
	display: flex;
}
.notification__box,
.notification__content {
	align-items: center;
}
.notification__box {
	animation: flyIn 0.3s ease-out;
	background-color: hsl(0,0%,100%);
	border-radius: 0.75em;
	box-shadow: 0 0.5em 1em hsla(var(--hue),10%,10%,0.1);
	height: 4em;
	transition:
		background-color var(--transDur),
		color var(--transDur);
}
.notification--out .notification__box {
	animation: flyOut 0.3s ease-out forwards;
}
.notification__content {
	padding: 0.375em 1em;
	width: 100%;
	height: 100%;
}
.notification__icon {
	flex-shrink: 0;
	margin-right: 0.75em;
	width: 2em;
	height: 2em;
}
.notification__icon-svg {
	width: 100%;
	height: auto;
}
.notification__text {
	line-height: 1.333;
}
.notification__text-title {
	font-size: 0.75em;
	font-weight: bold;
}
.notification__text-subtitle {
	font-size: 0.6em;
	opacity: 0.75;
}
.notification__btns {
	box-shadow: -1px 0 0 hsla(var(--hue),10%,10%,0.15);
	flex-direction: column;
	flex-shrink: 0;
	min-width: 4em;
	height: 100%;
	transition: box-shadow var(--transDur);
}
.notification__btn {
	background-color: transparent;
	box-shadow: 0 0 0 hsla(var(--hue),10%,10%,0.5) inset;
	font-size: 0.6em;
	line-height: 1;
	font-weight: 500;
	height: 100%;
	padding: 0 0.5rem;
	transition:
		background-color var(--transDur),
		color var(--transDur);
	-webkit-appearance: none;
	appearance: none;
	-webkit-tap-highlight-color: transparent;
}
.notification__btn-text {
	display: inline-block;
	pointer-events: none;
}
.notification__btn:first-of-type {
	border-radius: 0 0.75rem 0 0;
}
.notification__btn:last-of-type {
	border-radius: 0 0 0.75rem 0;
}
.notification__btn:only-child {
	border-radius: 0 0.75rem 0.75rem 0;
}
.notification__btn + .notification__btn {
	box-shadow: 0 -1px 0 hsla(var(--hue),10%,10%,0.15);
	font-weight: 400;
}
.notification__btn:active,
.notification__btn:focus {
	background-color: hsl(var(--hue),10%,95%);
}
.notification__btn:focus {
	outline: transparent;
}

@supports selector(:focus-visible) {
	.notification__btn:focus {
		background-color: transparent;
	}
	.notification__btn:focus-visible,
	.notification__btn:active {
		background-color: hsl(var(--hue),10%,95%);
	}
}

/* Dark theme */
@media (prefers-color-scheme: dark) {
	:root {
		--bg: hsl(var(--hue),10%,10%);
		--fg: hsl(var(--hue),10%,90%);
	}
	.notification__box {
		background-color: hsl(var(--hue),10%,30%);
	}
	.notification__btns {
		box-shadow: -1px 0 0 hsla(var(--hue),10%,90%,0.15);
	}
	.notification__btn + .notification__btn {
		box-shadow: 0 -1px 0 hsla(var(--hue),10%,90%,0.15);
	}
	.notification__btn:active,
	.notification__btn:focus {
		background-color: hsl(var(--hue),10%,35%);
	}

	@supports selector(:focus-visible) {
		.notification__btn:focus {
			background-color: transparent;
		}
		.notification__btn:focus-visible,
		.notification__btn:active {
			background-color: hsl(var(--hue),10%,35%);
		}
	}
}

/* Animations */
@keyframes flyIn {
	from {
		transform: translateX(calc(100% + 1.5em));
	}
	to {
		transform: translateX(0);
	}
}
@keyframes flyOut {
	from {
		transform: translateX(0);
	}
	to {
		transform: translateX(calc(100% + 1.5em));
	}
}