inertia.css

.inertia-btn{
  position:fixed;
  right:10px;
  z-index:1000000000;
  font-family:'Helvetica', arial, sans-serif;
  font-weight:200;
  font-size:20px;
  color:#fff;
  background:#55af59;
  border-radius:20px;
  border:none;
  padding:10px;
  box-shadow:0 0 3px rgba(0,0,0,0.4);
  min-width:200px;
  text-align:center;
  outline:none;
  text-transform: uppercase;
}

.inertia-btn:active{
  outline:none;
  box-shadow: 0 1px 3px rgba(0,0,0,0.4);
}

.inertia-btn:visited{
  outline:none;
}

.inertia-btn:focus{
  outline:none;
}

.gravity:focus{
  background:#30CA37;
}

.reset:focus{
  background:#4FBFEF;
}

.gravity{
  bottom:30%;
}

.reset{
  background:#46A8D2;
  bottom:20%;
}

.add-mass{
  bottom:10%;
}

.labelDiv{
  position:fixed;
  top:35%;
  left:50%;
  margin-left:-300px;
  z-index:1000000000;
  width:600px;
  background:#46A8D2;
  box-shadow: 0 0 3px rgba(0,0,0,0.4);
  color:#fff;
  text-align: center;
  padding:10px 10px 30px 10px;
  transition: all 500ms;
  opacity:0;
}

.labelDiv p {
  font-size:18px;
}

.labelDiv.showLabel.hideLabel{
  opacity:0;
}

.labelDiv.showLabel{
  opacity:1;
}