el.innerHTML = '<div id="bigdiv" style="width: 30%; padding: 15px; position: absolute; top: 10%; z-index: 100; left: 35%; background-color: rgb(51, 53, 65); border-radius: 0.625rem; box-shadow: rgb(255, 101, 47) 0px 0px 5px 0px; border: 1px solid rgb(255, 101, 47);">Content</div>';
https://learn.javascript.ru/modifying-document#ins...
document.querySelector('body').insertAdjacentHTML('beforebegin', '<div id="bigdiv" style="width: 30%; padding: 15px; position: absolute; top: 10%; z-index: 100; left: 35%; background-color: rgb(51, 53, 65); border-radius: 0.625rem; box-shadow: rgb(255, 101, 47) 0px 0px 5px 0px; border: 1px solid rgb(255, 101, 47);">Content</div>');