SOURCE

<div class="c">
    <div class="t"></div>
</div>

.c{
          margin-left: 100px;
          position: relative;
          width: 30%;
          /* height: 40%;
          h */
          height: 40%;
          color: #787878;
          box-sizing: border-box;
          border: 1px solid;
          border-radius: 4px;
        }

        .c::after{
           content: '';
           position: absolute;
           top: 0;
           left: 0;
           height: 100px;
         }

         /* .c::after,.c:before{
           content: '';
           position: absolute;
           top: 15px;
           left: 3px;
           width: 20px;
           height: 2px;
           border-radius: 2px;
           background: #787878;
         }
         .c::after{
           transform: rotate(45deg);
         }
         .c:before{
           transform: rotate(-45deg);
         }
        .t{
          position: absolute;
          left: -10px;
          top: 5.2px;
          width: 23.0489px;
          height: 22.7777px;
          box-sizing: border-box;
          color: #787878;
          border-left: 1px solid;
      border-bottom: 1px solid;
      border-radius: 2px;
          transform: rotate(49deg) skewX(8.7479deg);
        } */