Site-Wide Page Brightness Controls

This JavaScript snippet utilizes cookies to control the opacity of a fixed black overlay displayed across the site.
Hover the lightbulb below to try for yourself!

|May. 19, 12,021 11:39 pm|Modified:May. 20, 12,021|Portals
Brightness

CSS

#slOverlay {
	position: fixed;
	top: 0;
	right: 0;
	width: 100%;
	height: 100%;
	background: black;
	z-index: 99998;
	pointer-events: none;
	opacity: 0;
	-webkit-transition: all 0.5s ease;
	transition: all 0.5s ease;
}

.sl-wrap {
	display: block;
	position: relative;
	color: #333;
	max-width: 500px;
	margin: 30px auto;
	text-align: center;
	z-index: 9;
}

.sl-opacity-button .sl-icon {
	font-size: 0;
	position: relative;
}

.sl-opacity-button:hover .sl-icon::after {
	content: "";
	display: block;
	height: 50px;
	width: 150%;
	position: absolute;
	bottom: -25px;
	left: -25%;
}

.sl-opacity-button {
	cursor: pointer;
}
.sl-opacity-button .sl-icon::before {
	content: "";
	font-family: 'light-icons';
	font-size: 45px;
	font-weight: normal !important;
}

.sl-opacity-button:hover::after{
	content: "";
	display: block;
	width: 292px;
	position: absolute;
	height: 50px;
	left: 105px;
	bottom: -10px;
	cursor: default;
	z-index: -1;
}

.sl-selector {
	position: absolute;
	left: 105px;
	top: 100%;
	width: 292px;
	padding: 10px;
	background: #222;
	border-radius: 6px;
	opacity: 0;
	pointer-events: none;
	border: 1px outset #222;
	box-shadow: 0 3px 5px rgba(0,0,0,0.35);
	-webkit-transition: all 0.3s ease;
	transition: all 0.3s ease;
}

.sl-selector::before {
	content: "";
	display: block;
	position: absolute;
	left: 129px;
	top: -30px;
	width: 0;
	height: 0;
	border: 15px solid transparent;
	border-bottom-color: #222;
}

.sl-opacity-button:hover .sl-selector {
	opacity: 1;
	pointer-events: all;
}

.sl-selector button {
	cursor: pointer;
	background: white;
	border: none;
	border-right: 1px solid #111;
	color: #111;
	width: 45px;
	font-size: 12px;
	font-family: inherit;
	padding: 3px;
	position: relative;
	overflow: hidden;
	-webkit-transition: all 0.2s ease;
	transition: all 0.2s ease;
}

.sl-selector button:hover {
	opacity: 0.9;
	transform: translateY(-1px);
	box-shadow: 0 2px 2px rgba(0,0,0,0.5);
}

.sl-selector button::before {
	content: "";
	position: absolute;
	top: 0;
	left: 0;
	width: 100%;
	height: 100%;
	pointer-events: none;
	background: black;
	opacity: 0;
}

.sl-selector button:first-of-type {
	border-radius: 4px 0 0 4px;
}
.sl-selector button:last-of-type {
	border-radius: 0 4px 4px 0;
}

.sl-selector > span {
	cursor: default;
	display: block;
	line-height: 1em;
	padding-bottom: 2px;
	font-size: 12px;
	text-align: left;
	color: white;
}

.sl-selector #slCurrent {
	font-weight: bold;
}

#slLight50::before {opacity: 0.5;}
#slLight60::before {opacity: 0.4;}
#slLight70::before {opacity: 0.3;}
#slLight80::before {opacity: 0.2;}
#slLight90::before {opacity: 0.1;}

JavaScript

const opacityValue = document.cookie.split('; ').find(row => row.startsWith('slOpacity=')).split('=')[1];

window.onload = function() {
        if (document.cookie.split(';').some((item) => item.includes('slOpacity='))) {
        document.getElementById("slOverlay").style="opacity:"+opacityValue+"%";
        var slOpacityBtn = document.getElementsByClassName("sl-opacity-button")[0];

        slOpacityBtn.innerHTML+='<div class="sl-selector">
                <span>Current Brightness: <span id="slCurrent">100%</span></span>
                <button id="slLight100">100%</button>
                <button id="slLight90">90%</button>
                <button id="slLight80">80%</button>
                <button id="slLight70">70%</button>
                <button id="slLight60">60%</button>
                <button id="slLight50">50%</button>
                </div>';

        document.getElementById("slLight100").setAttribute("onclick", "setOpacity('slOpacity', '0')");
        document.getElementById("slLight90").setAttribute("onclick", "setOpacity('slOpacity', '10')");
        document.getElementById("slLight80").setAttribute("onclick", "setOpacity('slOpacity', '20')");
        document.getElementById("slLight70").setAttribute("onclick", "setOpacity('slOpacity', '30')");
        document.getElementById("slLight60").setAttribute("onclick", "setOpacity('slOpacity', '40')");
        document.getElementById("slLight50").setAttribute("onclick", "setOpacity('slOpacity', '50')");

        var slCurrentOpacity = document.getElementById("slCurrent");
        var slOpacityPercent = 100 - opacityValue;
        slCurrentOpacity.innerHTML = slOpacityPercent + "%";
} else {
        document.cookie = "slOpacity=0; path=/";
        window.location.reload();
}}

function setOpacity(cname,cvalue) {
        document.cookie = cname+"="+cvalue+"; path=/";
        window.location.reload();
}