.border {
    position: relative;
}
.border::after {
     content: '';
     position: absolute;
     width: 200%;
     height: 200%;
     left: -50%;
     top: -50%;
     border: 1px solid #000;
     border-radius: 4px;
     transform: scale(0.5);
     box-sizing: border-box;
 }