inst/reveal.js-4.2.1/plugin/customcontrols/style.css

#customcontrols {
	z-index: 40;
	position: fixed; 
	left: 70px; 
	bottom: 30px;
	text-align: center;
	font-size: 24px;
}

#customcontrols button {
	background: none;
	color: var(--r-link-color);
	border: none;
	padding: 0;
	font: inherit;
	cursor: pointer;
	outline: inherit;
	z-index: 40;
}

#customcontrols button:hover {
	color: var(--r-link-color-hover);
}

#customcontrols > ul {
	position: fixed; 
	left: 54px; 
	bottom: 64px;
	list-style-type: none;
	overflow: hidden;
	margin: 0;
	padding: 0;
	border: 1px solid var(--r-link-color);
	border-radius: 5px;
	padding: 10px;
	background-color: var(--r-background-color)
}

#customcontrols ul > li {
	margin: 0px 5px;
	padding: 0px 5px;
	float: left;
}

#customcontrols.collapsed  #collapse-customcontrols, #customcontrols.collapsed > ul  {
	display: none;
} 

#customcontrols:not(.collapsed) #expand-customcontrols {
	display: none;
} 

@media only screen and (min-width: 500px) {
	#customcontrols > button {
		display: none;
	}
	#customcontrols > ul {
		bottom: 20px;
		border: none;
		background: none;
	}
}