先看效果图

HTML代码（注：view是微信小程序中的div，如果是html或者vue换成div即可）：

<view style="width:272rpx;height:216rpx;position:relative;margin: 10px 0px 0 5px;">
   <view class="a"></view>
   <view class="b"></view>
   <view class="c"></view>
   <view class="d"></view>
</view>

CSS代码：

.a {
    width: 10px;
    height: 10px;
    position: absolute;
    top: 0;
    left: 0;
    border-left: 2px solid #EBEBEB;
    border-top: 2px solid #EBEBEB;
}

.b {
    width: 10px;
    height: 10px;
    position: absolute;
    top: 0;
    right: 0;
    border-right: 2px solid #EBEBEB;
    border-top: 2px solid #EBEBEB;
}

.c {
    width: 10px;
    height: 10px;
    position: absolute;
    bottom: 0;
    left: 0;
    border-bottom: 2px solid #EBEBEB;
    border-left: 2px solid #EBEBEB;
}

.d {
    width: 10px;
    height: 10px;
    position: absolute;
    bottom: 0;
    right: 0;
    border-right: 2px solid #EBEBEB;
    border-bottom: 2px solid #EBEBEB;
}

即可实现效果。