CSS如何设置多重边框

<div class="div1">div1</div>
<div class="div2">div2</div>

1. box-shadow

语法：box-shadow: h-shadow v-shadow blur spread color inset;

.div1{
    width: 200px;
    height: 50px;
    border: 5px solid red;
    margin: 20px;
    box-shadow: 0 0 0 10px green;
}

2. outline

语法：outline：outline-color outline-style outline-width inherit

.div2{
    width: 200px;
    height: 50px;
    border: 5px solid blue;
    margin: 20px;
    outline: 5px solid pink;
    outline-offset: 0px;
}

效果图：