如图示红色边框，选择input的效果该怎么写

Question

图示红色部分，选择效果用css怎么写

Answer 1

四个角定各位个定位一个透明的方块，方块各加两条边

    <style>
        .item{
            height: 50px;
            width: 250px;
            background: #ccc;
            position: relative;
        }
        .item-horn{
            position: absolute;
            width: 20px;
            height: 20px;
        }
        .item-left-top{
            top: 0;
            left: 0;
            border-top: 2px solid red;
            border-left: 2px solid red;
        }
        .item-right-top{
            top: 0;
            right: 0;
            border-top: 2px solid red;
            border-right: 2px solid red;
        }
        .item-left-bottom{
            bottom: 0;
            left: 0;
            border-bottom: 2px solid red;
            border-left: 2px solid red;
        }
        .item-right-bottom{
            bottom: 0;
            right: 0;
            border-bottom: 2px solid red;
            border-right: 2px solid red;
        }
    </style>
    
    
        
    <div class="item">
        <div class="item-horn item-left-top"></div>
        <div class="item-horn item-right-top"></div>
        <div class="item-horn item-left-bottom"></div>
        <div class="item-horn item-right-bottom"></div>
    </div>