.dummy {
    box-sizing: border-box;
    display: inline-block; 
    position: relative;
  }
  .dummy:before {
    content: '';
    position: absolute;
    background: lightgray;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
  }
  .dummy:after { 
    content: attr(width) " x " attr(height);
    white-space: pre;
    color: gray;
    text-align: center;
    display: block;
    position: absolute;
    width: 100%;
    top: calc(50% - .5em);
    font-size: 100%;
  }
  .dummy.alt:after {
    content: attr(alt);
  }
  .dummy.double.alt:after {
    content: attr(alt) "\A" attr(data-second);
    white-space: pre;
    top: calc(50% - 1em);
  }
  .dummy.big {
    font-size: 200%;
  }
  .dummy.small {
    font-size: 50%;
  }
  .dummy.round {
    padding: 0 1em;
  }
  .dummy.round:before { 
    border-radius: 1em;
  }
  .dummy.round:after {
    margin-left: -1em;
  }