nextcloud/apps/dashboard/css/dashboard.scss

#header {
	background: transparent !important;
	--color-header: rgba(24, 24, 24, 1);

	#body-user.dashboard--dark & {
		--color-header: rgba(255, 255, 255, 1);
	}

	// Show gradient below navigation for visibility of icons when scrolled
	&:before {
		content: ' ';
		display: block;
		position: absolute;
		background-image: linear-gradient(180deg, var(--color-header) 0%, transparent 100%);
		width: 100%;
		height: 70px;
		top: 0;
		margin-top: -70px;
		transition: margin-top var(--animation-slow);

		#body-user.dashboard--scrolled & {
			margin-top: 0;
		}
	}

	// Use flat color instead of gradient for high contrast theme
	#body-user.theme--highcontrast & {
		background-color: var(--color-header) !important;

		&:before {
			display: none;
		}
	}
}

// Move content up so it scrolls below navigation
#content {
	padding-top: 0 !important;
}

// Hide triangle indicators from navigation since they are out of place without the header bar
#appmenu li a.active::before,
#appmenu li:hover a::before,
#appmenu li:hover a.active::before,
#appmenu li a:focus::before {
	display: none !important;
}

$has-custom-logo: variable_exists('theming-logo-mime') and $theming-logo-mime != '';

body.dashboard--inverted:not(.dashboard--dark) {
	// Do not invert the default logo
	@if ($has-custom-logo == false) {
		$image-logo: url(icon-color-path('logo', 'logo', #ffffff, 1, true));
		#header .logo {
			background-image: $image-logo !important;
			opacity: 1;
		}
	}

	#app-dashboard > h2 {
		color: #fff;
	}
	#appmenu li span {
		color: #fff;
	}
	#appmenu svg image {
		filter: invert(0);
	}
	#appmenu .icon-more-white,
	.header-right > div:not(#settings) > *:first-child {
		filter: invert(1) hue-rotate(180deg);
	}
}

body.dashboard--dark:not(.dashboard--inverted) {
	// invert the default logo
	@if ($has-custom-logo == false) {
		$image-logo: url(icon-color-path('logo', 'logo', #000000, 1, true));
		#header .logo {
			background-image: $image-logo !important;
			opacity: 1;
		}
	}

	#app-dashboard > h2 {
		color: #000;
	}
	#appmenu li span {
		color: #000;
	}
	#appmenu svg {
		filter: invert(1) hue-rotate(180deg) !important;
	}
	#appmenu .icon-more-white,
	.header-right > div:not(#settings) > *:first-child {
		filter: invert(1) hue-rotate(180deg) !important;
	}
}