CSS篇之炫酷框

加上背景之后就是下图：

 实现原理：div大小为20px 20px;那么伪元素大小要比div大出一圈，才能显示出边框；

在鼠标滑过的时候，动态更改伪元素的背景色位置

   <div id="b" class="b"></div>

*{
  --border: 4px;
 border:none;
}

.b{
  width:200px;
  height:200px;
  border:1px solid black;
  box-sizing:border-box;
   position: relative;
  background:#999;
}
.b::after {
  content: "";
  display: block;
  width: calc(100% + var(--border) * 2);
  height: calc(100% + var(--border) * 2);
  position: absolute;
  z-index: -1;
  background-image: var(--bg);
  left:calc(var(--border) * -1);
  top:calc(var(--border) * -1);
}

  const b=document.getElementById('b');
b.addEventListener("mousemove", e=>{
 let rect = b.getBoundingClientRect();
   let x = e.pageX - rect.left;
    let y = e.pageY - rect.top;
  b.style.setProperty(
          "--bg",
          `radial-gradient(100px at ${x}px ${y}px, rgba(186, 10, 244, 0.5), rgba(255, 255, 255, 0))`
        );
})

上面是一个dom情况，如果多个dom,可遍历dom,更改radial-gradient属性；一下是多个dom的效果展示：

多个dom的遍历代码：

window.addEventListener("mousemove", (e) => {
  let bt = document.querySelectorAll(".b");
  for (let i = 0; i < bt.length; i++) {
    let rect = bt[i].getBoundingClientRect();
    let x = e.pageX - rect.left;
    let y = e.pageY - rect.top;
    bt[i].style.setProperty(
          "--afterBack",
          `radial-gradient(100px at ${x}px ${y}px, rgba(186, 10, 244, 0.5), rgba(255, 255, 255, 0))`
        );
  }
});