.block {
   width: 100px;
   height: 100px;
   /* dashed border */
   background-image: url("data:image/svg+xml,%3csvg width='100%25' height='100%25' xmlns='http://www.w3.org/2000/svg'%3e%3crect width='100%25' height='100%25' fill='none' stroke='%23333' stroke-width='4' stroke-dasharray='6%2c 14' stroke-dashoffset='0' stroke-linecap='square'/%3e%3c/svg%3e");
}