Horizontally align divs

HTML

<div id='resizeDiv'>

</div>

CSS

#resizeDiv {
    background-color: skyblue;
    width: 100%;
    float: left;
}

JavaScript

var scale1 = 1080/1920; //if width is always bigger than height
var originalWidth = document.getElementById('resizeDiv').offsetWidth;
document.getElementById('resizeDiv').setAttribute("style","height:" + originalWidth*scale1 + 'px');



var originalHeight = document.getElementById('resizeDiv').offsetHeight;

var scale2 = originalWidth/originalHeight; 

//var scale1 = 1920/1080; //if height is always bigger than width
//var scale2 = originalWidth/originalHeight; 

window.onresize = function(event) {
    var getWidth = document.getElementById('resizeDiv').offsetWidth;

    document.getElementById('resizeDiv').setAttribute("style","height:" + getWidth*scale1 + 'px');
};