Use the focus-within pseudo-class to conditionally assign styling to a parent element when its child receives focus. HTML: import "./styles.css"; document.getElementById("app").innerHTML = ` <ul id="red"> <li> <
var obj=document.getElementById("btn");var currentStyle=null;if(obj.currentStyle){ currentStyle=obj.currentStyle;}else{ currentStyle=window.getComputedStyle(obj,null);}alert(currentStyle.width); var addCssRule = function() { // 创建一个 style, 返回其 s