.signal 
{
  display: inline-block;
  width: 1rem;
  height: 1rem;
  border-radius: 50%;
  background-color: #757575;
  vertical-align: middle;
}

.signal--down 
{
  background-color: #ff0000;
}

.signal--running 
{
  background-color: #00ff00;
}