<!DOCTYPE html>
<html lang="en" >
<head>
  <meta charset="UTF-8">
  <title>CodePen - Shadow cast spotlight</title>
  <link rel="stylesheet" href="./style.css">

</head>
<body>
<!-- partial:index.partial.html -->
<div id="container">
    <div id="title">Move your cursor over the box to cast a shadow with the spotlight.</div>
    <div id="box">
        <div class="shadow__wall">
            <div class="shadow__box" id="shadow__box--back"></div>
            <p id="shadow__text">12:34:56</p>
            <div class="shadow__box" id="shadow__box--front"></div>
        </div>
        <div id="shadow__spot"></div>
    </div>
</div>
<!-- partial -->
  <script  src="./script.js"></script>
  
</body>
</html>

* {
    box-sizing: border-box;
}

html, body {
    margin: 0;
    padding: 0;
}

body {
    background: black;
    color: #f28282;
    font-family: sans-serif;
    font-size: 16px;
    overscroll-behavior: none;
    
    display: flex;
    flex-direction: column;
    align-items: center;
    height: 100vh;
}

#container {
    width: 100vw;
    height: 100vh;
}

#title {
    text-align: center;
    width: 100%;
    padding: 10px 0 10px 0;
}

#box {
    position: relative;
    width: 100%;
    height: 100%;
    background: #ff0303;
    overflow: hidden;
    /*cursor: none;*/
    border: 1px solid #333;
    
    -webkit-tap-highlight-color: rgba(0,0,0,0);
  -webkit-user-select: none;
}

.shadow__wall {
    position: absolute;
    top: 50%;
    left: 0;
    width: 100%;
}

#shadow__text {
    position: absolute;
    width: 100%;
    margin: 0;
    color: #06a9d2;
    font-family: Helvetica, Arial, sans-serif;
    font-size: 5rem;
    font-weight: bold;
    text-align: center;
    white-space: nowrap;
}

.shadow__box {
    position: absolute;
    background: #c85151;
    top: 4.5rem;
    height: 50vh;
}

#shadow__box--back {
    left: -5%;
    width: 110%;
}

#shadow__box--front {
    left: 0;
    width: 100%;
}

#spotlight {
    position: fixed;
    top: 0;
    left: 0;
    height: 100vh;
    width: 100vw;
  
    -webkit-mask-composite: destination-out;
    mask-composite: exclude;
    z-index: 1;
  }
#shadow__spot {
    position: absolute;
    top: 0;
    left: 0;
    width: 200%;
    height: 200%;
    background: -webkit-gradient(radial, center center, 0, center center, 250, from(rgba(0,0,0,0)), to(rgba(0,0,0,1)));
}
const textElem = document.querySelector('#shadow__text');
const spotElem = document.querySelector('#shadow__spot');
const boxElem = document.querySelector('#shadow__box--back');

const container = document.querySelector('#box');
var width = container.offsetWidth;
var height = container.offsetHeight;

const relMousePos = {
    _x: 0, _y: 0, x: 0, y: 0,
    updatePos: function(e) {
        const event = (e || window.event) && (e.touches && e.touches[0]) || e;
        this.x = event.clientX - this._x;
        this.y = event.clientY - this._y;
    },
    setOrigin: function(e) {
        this._x = e.offsetLeft + Math.floor(e.offsetWidth / 2);
        this._y = e.offsetTop + Math.floor(e.offsetHeight / 2);
    }
}
relMousePos.setOrigin(container);
container.addEventListener('mousemove', relMousePos.updatePos);

function updateSize(e) {
    width = container.offsetWidth;
    height = container.offsetHeight;
    relMousePos.setOrigin(container);
    
    onMouseMove({clientX: relMousePos._x, clientY: relMousePos._y + 25});
}

function updateTime() {
    let date = new Date();
    let time = date.toLocaleTimeString();
    textElem.innerText = time;
    
    setTimeout(updateTime, 1000);
}

function onMouseMove(e) {
    relMousePos.updatePos(e);
    
    var xm = relMousePos.x;
    var ym = relMousePos.y;

    var d = Math.round(Math.sqrt(xm*xm + ym*ym) / 10);
    textElem.style.textShadow = -xm + 'px ' + -ym + 'px ' + (d + 10) + 'px black';    
    boxElem.style.boxShadow = '0 ' + -ym + 'px ' + (d + 30) + 'px black';    
    spotElem.style.backgroundPosition = (xm - (width / 2)) + 'px ' + (ym - (height / 2)) + 'px';
}

function init() {  
    updateTime();
    
    container.addEventListener('mousemove', onMouseMove);
    container.addEventListener('touchmove', function (e) {
        e.preventDefault();
        e.stopPropagation();
        onMouseMove(e);
    }, {passive: false});
    
    onMouseMove({clientX: relMousePos._x, clientY: relMousePos._y + 25});
}

document.addEventListener('resize', updateSize);
document.addEventListener('DOMContentLoaded', init);

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.