A diagonal line through a box

diagonalline.scss

.container {

  position: relative;
  overflow: hidden;

  &:after {
    
    position: absolute;
    content: ' ';
    width: 100%;
    height: 200%;
    border: 1px solid black;
    bottom: 0;
    left: 0;
    transform-origin: bottom left;
    transform: rotateZ(45deg);
    
  }
}