index.css

.button {
      background-color: #4CAF50; /* Green */
      border: none;
      color: white;
      padding: 16px 16px;
      text-align: center;
      text-decoration: none;
      display: inline-block;
      font-size: 16px;
      margin: 4px 2px;
      -webkit-transition-duration: 0.4s; /* Safari */
      transition-duration: 0.4s;
      cursor: pointer;
      /*box-shadow: 0 9px #999;*/
    }
    .button1 {
      background-color: white; 
      color: black; 
      border: 2px solid #f44336;
    }
    .button1:hover {
      background-color: #f44336;
      color: white;
    }
    .button2 {
      background-color: white; 
      color: black; 
      border: 2px solid #008CBA;
    }
    .button2:hover {
      background-color: #008CBA;
      color: white;
    }
    .button3 {
      background-color: white; 
      color: black; 
      border: 2px solid #4CAF50;
    }
    .button3:hover {
      background-color: #4CAF50;
      color: white;
    }
    .button4 {
      background-color: white; 
      color: black; 
      border: 2px solid #f4511e;
    }
    .button4:hover {
      background-color: #f4511e;
      color: white;
    }