window.onload=function(){
let modalCss = '<style>#oxModalMain {position: fixed;background: rgba(0, 0, 0, 0.8);top: 0;display: flex;align-items: center;left: 0;width: 100%;height: 100%;justify-content: center;}#oxModalBody {background: #fff;padding: 25px;width: 50%;}@media  only screen and (max-width: 600px) {#oxModalBody {width: 80%;}}</style>';
let modalHtml = '<div id="oxModalBody">Helloo</div>';

var cssNode = document.createElement("div");
cssNode.innerHTML = modalCss;
document.body.appendChild(cssNode);

var node = document.createElement("div");
node.setAttribute("id", "oxModalMain");
node.innerHTML = modalHtml;
document.body.appendChild(node);
}