WordPress/wp-content/themes/twentytwentyone/assets/css/style-dark-mode.css

/* OS dark theme preference */
@media only screen {

	.is-dark-theme.is-dark-theme {
		--global--color-background: var(--global--color-dark-gray);
		--global--color-primary: var(--global--color-light-gray);
		--global--color-secondary: var(--global--color-light-gray);
		--button--color-text: var(--global--color-background);
		--button--color-text-hover: var(--global--color-secondary);
		--button--color-text-active: var(--global--color-secondary);
		--button--color-background: var(--global--color-secondary);
		--button--color-background-active: var(--global--color-background);
		--global--color-border: #ffffff8c;
	}

	.is-dark-theme.is-dark-theme .site a:focus,
	.is-dark-theme.is-dark-theme .site a:focus .meta-nav {
		background: #000;
		color: #fff;
		text-decoration: none;
	}

	.is-dark-theme.is-dark-theme img {
		filter: brightness(0.85) contrast(1.1);
	}

	.respect-color-scheme-preference.is-dark-theme body {
		background-color: var(--global--color-background);
	}

	#dark-mode-toggler {
		cursor: pointer;
		display: flex;
		align-items: center;
		justify-content: center;
		font-size: var(--global--font-size-xs);
		padding: 0.5em;
		min-height: 44px;
		min-width: max-content;
		border: 2px solid currentColor;
		box-shadow: none;
		background: var(--button--color-text);
		color: var(--button--color-background);
		z-index: 9998;
	}

	.no-js #dark-mode-toggler {
		display: none;
	}

	.wp-admin #dark-mode-toggler {
		display: none;
	}

	#dark-mode-toggler.fixed-bottom {
		position: fixed;
		bottom: 5px;
		right: 5px;
		transition: bottom 0.5s;
	}

	#dark-mode-toggler.fixed-bottom.hide:not(:focus) {
		bottom: -80px;
	}

	#dark-mode-toggler.relative {
		position: absolute;
		height: 44px;
		top: calc(2.4 * var(--global--spacing-vertical) - 44px);
		right: calc(50vw - var(--responsive--alignwide-width) / 2 - 0.5em);
	}

	.admin-bar #dark-mode-toggler.relative {
		top: calc(2.4 * var(--global--spacing-vertical) - 44px + 32px);
	}
}
@media only screen and (max-width: 782px) {

	.admin-bar #dark-mode-toggler.relative {
		top: calc(2.4 * var(--global--spacing-vertical) - 44px + 46px);
	}
}
@media only screen and (max-width: 481px) {

	.admin-bar #dark-mode-toggler.relative {
		top: calc(2.4 * var(--global--spacing-vertical) - 44px + 26px);
	}
}
@media only screen and (max-width: 481px) {

	body:not(.primary-navigation-open) #dark-mode-toggler.relative ~ nav {
		top: calc(44px + 44px);
	}
}
@media only screen {

	.primary-navigation-open #dark-mode-toggler {
		display: none;
	}
}
@media only screen {

	#dark-mode-toggler:hover,
	#dark-mode-toggler:focus {
		color: var(--button--color-background-active);
		border: 2px solid var(--button--color-text-active);
		background-color: var(--button--color-text-active);
	}
}
@media only screen {

	.is-IE #dark-mode-toggler {
		display: none;
	}
}