.range-slider {
  width:100%;
  height:1.2em;
  margin-left:0.5em;
  top:0.2em;
  margin-right:0.5em;
  position:relative;
  cursor:pointer;
}
.range-slider:before {
  content:"";
  display:block;
  position:absolute;
  top:50%;
  left:0;
  width:100%;
  height:1px; 
  background-color:black;
}
.range-slider span {
  display:block;
  height:inherit;
  position:relative;
  z-index:20;
  background-color:rgba(100,50,50,0.5);
  cursor:inherit;
}