<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
#cont{
width: 500px;
height: 500px;
}
#cont > div{
float: left;
width: 100px;
height: 100px;
}
</style>
</head>
<body>
<script>
document.body.insertAdjacentHTML('beforeend', '<div id="cont">'+'<div></div>'.repeat(25)+'</div>');
document.querySelectorAll('#cont>div').forEach(el=>{
el.style.backgroundColor = '#'+Math.random().toString(16).slice(2,8);
el.onclick = e => el.style.display = 'none';
});
</script>
</body>
</html>