wiggle box

HTML

<div id="box"></div>

JavaScript

function insertStyleSheetRule(ruleText)
{
    let sheets = document.styleSheets;
    
    if(sheets.length == 0)
    {
        let style = document.createElement('style');
        style.appendChild(document.createTextNode(""));
        document.head.appendChild(style);
    }
    
    let sheet = sheets[sheets.length - 1];
    sheet.insertRule(ruleText, sheet.rules ? sheet.rules.length : sheet.cssRules.length);
}

insertStyleSheetRule("@keyframes spinIt { 0% { transform: rotate(-20deg); } 100% { transform: rotate(20deg); } }");

insertStyleSheetRule("#box { " + 
    "animation: spinIt 1s infinite alternate cubic-bezier(0.5,0,0.5,1); " + 
    "width: 64px; height: 64px; background-color: red; border: 4px solid black; " + 
"}");