CSS Fill Blue Button Animation With Code

 
.button {
  background-color: #4CAF50; 
  font-size: 13px;
  -webkit-transition-duration: 0.3s;
  transition-duration: 0.2s;
  padding: 38px;
  -webkit-transition-duration: 0.3s;
  transition-duration: 0.3s;
}  

.button_name {
    padding-top: 0.3em;
    padding-bottom: 0.3em;
    background-color: #d9d9d9;
    border-top-left-radius: 10px;
    border-bottom-left-radius: 10px;
    border-top-right-radius: 10px;
    border-bottom-right-radius: 10px;
    border: 4px solid #4db8ff;

}

.button_name:hover {
  background-color: #4db8ff;
}

Button Animations CSS (w/ code)