main.css

@keyframes bounce{
    0%, 20%, 60%, 100%{
        -webkit-transform: translateY(0);
        transform: translateY(0);
    }
    40%{
        -webkit-transform: translateY(-20px);
        transform: translateY(-20px);
    }
    80%{
        -webkit-transform: translateY(-10px);
        transform: translateY(-10px);
    }

}

.botoes{
    text-align: center;
    margin-top: 50px;
}
.efeito{
    border:none;
    color:whitesmoke;
    padding:20px;
    margin: 20px;
    font-size: 24px;
    border-radius: 50px;
    position: relative;
    box-sizing: border-box;
    cursor: pointer;
    transition: all 400ms ease;
}

.efeito-1{
    background: #009c3d;
    
}
.efeito-1:hover{
    background-color: rgba(0, 0, 0, 0);
    color: #009c3d;
    box-shadow: inset 0 0 0 3px #009c3d;
}

.efeito-2{
    background: #f18f01;

}

.efeito-2:hover{
    animation: bounce 1s; /* chama o keyframe criado */
}

.efeito-3{
    background: #376693;
    transform-style: preserve-3d;

}

.efeito-3:after{

    top: -100%;
    left: 0px;
    width: 100%;
    padding: 20px;
    position: absolute;
    background: #3a9999;
    border-radius: 50px;
    box-sizing: border-box;
    content: "Mudou!";
    transform-origin: left bottom;
    transform: rotateX(90deg);

}

.efeito-3:hover{
    transform-origin: center bottom;
    transform: rotateX(-90deg) translateY(100%);
}