style.css

body{
    background: #333;
    margin: 0;
    padding: 0;
}

.container{
    text-align: center;
    margin-top: 360px;
}

.btn{
    border: 1px solid cornflowerblue;
    background: none;
    padding: 10px 20px;
    font-size: 20px;
    font-family: 'Gill Sans';
    cursor: pointer;
    margin: 10px;
    transition: 0.8s;
    position: relative;
    overflow: hidden;
}

.btn1,.btn2{
    color: #3498bd
}

.btn3, .btn4{
    color:#fff
}

.btn1:hover, .btn2:hover{
    color: #fff;
}

.btn3:hover, .btn4:hover{
    color:#3498bd
}

.btn5{
    color: #3498bd
}

.btn5:hover{
    color: #fff;
}

.btn::before{
    content: "";
    position: absolute;
    left: 0;
    width: 100%;
    height: 0%;
    background: cornflowerblue;
    z-index: -1;
    transition: 0.8s;
}

.btn1::before, .btn3::before{
    top: 0;
    border-radius: 0 0 50% 50%;
}

.btn2::before, .btn4::before{
    bottom: 0;
    border-radius: 50% 50% 0 0;
}

.btn5::before{
    top: 0;
    border-radius: 0 50% 50% 0;
}

.btn5:hover::before{
    height: 180%;
}

.btn3::before, .btn4::before{
    height: 180%;
}

.btn1:hover::before, .btn2:hover::before{
    height: 180%;
}


.btn3:hover::before, .btn4:hover::before{
    height: 0;
}