Как сделать "ступеньку"?

#test {
  position: absolute;
  right: 40px;
  bottom: 20px;
  height: 20px;
  width: 40px;
  background-image: url(https://i.stack.imgur.com/pzjeJ.png);
  background-repeat: no-repeat;
  background-position: -105px -60px;
  background-color: yellow;
}
#box {
  position: relative;
  width: 158px;
  height: 107px;
  border: 1px solid;
}
#right {
  right: 0;
  bottom: 20px;
  width: 40px;
  background-color: #000;
}
#bottom {
  bottom: 0;
  width: 100%;
}
#right, #bottom {
  position: absolute;
  height: 20px;
  background-color: #000;
}

<div id='box'>
  <div id='test'></div>
  <div id='right'></div>
  <div id='bottom'></div>
</div>