• HTML
• CSS
• JS

HTML

<div id="numero"></div>

CSS

body{
    background:#34495e;
}
#numero{
    font-size:200px;
    color:#d6dbdf;
    text-align:center;
}

JS

var cont= 0;
var num = document.getElementById("numero");

window.setInterval(function(){
    num.innerHTML = cont;
    cont++;
},1000);