body {
    margin: 0;
    padding: 0;
    font-size: 75px;
    text-align: center;
}
  
  
h1 {
    font-size: 35px;
    color: green;
    text-align: center;
}
  
.container {
    text-align: center;
    margin-top: 150px;
}
 
.btn {
    background: none;
    border: 1px solid green;
    font-size: 23px;
    padding: 10px 20px;
    font-family: "montserrat";
    cursor: pointer;
    margin: 10px;
    transition: 0.8s;
    position: relative;
    overflow: hidden;
}
  
.btn1,
.btn2 {
    color: green;
}
  
.btn1:hover,
.btn2:hover {
    color: #fff;
}
  
.btn::before {
    content: "";
    position: absolute;
    left: 0;
    width: 100%;
    height: 0%;
    background: green;
    z-index: -1;
    transition: 0.8s;
}
  
.btn1::before {
    top: 0;
    border-radius: 0 0 50% 50%;
}
  
.btn2::before {
    bottom: 0;
    border-radius: 50% 50% 0 0;
}
  
.btn1:hover::before,
.btn2:hover::before {
    height: 180%;
}