.battery {
  width: 80px;
  height: 40px;
  position: relative;
  margin: 10px;
  background-color: #f3f3f3;   
  border: 2px solid #333;
  border-radius: 8px;
  overflow: hidden;
}
.battery:before {
  content: '';
  position: absolute;
  width: 70px;
  height: 40px;
  background-color: #333;
  border-radius: 5px;
}
.green:before {
  width: 80px;
  background-color: #4CAF50;
}

.yellow:before {
  width: 40px;
  background-color: #FFEB3B;
}

.red:before {
  width: 20px;
  background-color: #F44336;
}