style.css

@import url('https://fonts.googleapis.com/css2?family=Roboto:ital@1&display=swap');
* {
    margin: 0;
    box-sizing: border-box;
    font-family: 'Roboto', sans-serif;
}
html {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100%;
    width: 100%;
    background-image: linear-gradient(to bottom right, #000000, #070739);   
}
body {
    perspective: 800px;
}
.btn {
    position: relative;
    height: 150px;
    width: 450px;
    transform-style: preserve-3d;
    transition: transform 400ms ease-in-out;
    transform: translateZ(-75px);
}
.btn:hover {
    transform: rotateX(-90deg) translateY(75px);
} 
.side {
    position: absolute;
    width: 100%;
    height: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 3.5em;
    font-weight: bold;
    backface-visibility: hidden;
}
.default-side {
   background-image: linear-gradient(to bottom right, #f7e8f6 , #fe59d7);
   border: 10px solid #9d0b28;
   color: #9d0b28;
   transform: translateZ(75px);
}
.hover-side {
    color: #e5b0ea;
    background-image: linear-gradient(to bottom right, #ff004d ,  #9d0b28);
    transform: rotatex(90deg) translateZ(75px);
    
}