@mixin tagElement($color) {
   position: relative;
   & > div.dbg {
      position: absolute;
      top: -18px; right: 10px;
      margin: 0; border: 0;
      padding: 0 0.5em;
      background-color: transparentize($color, 0.5);
      font-size: 75%;
      font-weight: normal;
      color: white;
   }
}

button#debug-toggle {
   position: fixed;
   top: 0;
   right: 0;
   width: auto;
   z-index: 10;
}

div#test {
   div, span {
      margin: 1em;
      border: 1px solid transparent;
      padding: 1em;
   }
   &.debug {
      div {
         border-color: dimgray;
         @include tagElement(dimgray);
      }
      span {
         border-color: deeppink;
         @include tagElement(deeppink);
      }
   }
   div.blue {
      font-weight: bold;
      color: blue;
      border: 2px solid blue;
   }
}