style.css

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
body {
    transform-style: preserve-3d;
    perspective: 2000px;
    overflow: hidden;
}

div#first {
    position: absolute;
    width: 100%;
    height: 100vh;
    /* background-color: #f3c5ff; */
    background: repeating-linear-gradient(90deg,#4b4453 5%,#926c00 10%);
    transition: all 3s ease-in-out;
    /* transform-style: preserve-3d; */
    /* perspective: 1000px; */
    /* animation: animate1 2s ease-in-out ; */
}
div#second {
    position: absolute;
    width: 100%;
    height: 100vh;
    background: repeating-linear-gradient(90deg,#4b4453 5%,#926c00 10%);
    transition: all 3s ease-in-out;
    /* transform-style: preserve-3d; */
    /* perspective: 1000px; */
    /* animation: animate2 2s ease-in-out ; */
}

div#first {
    right: 50%;
}
div#second {
    left: 50%;
}
#btn {
    position: absolute;
    top: 50vh;
    left: 50vw;
    z-index: 2;
    margin-left: -3.5rem;
    height: 3rem;
    width: 7rem;
    border: none;
    border-radius: 10px;
    background-color: #ff8066;
    cursor: pointer;
    transition: all 0.5s ease-in-out;
    font-family: 'Trebuchet MS', 'Lucida Sans Unicode', 'Lucida Grande', 'Lucida Sans', Arial, sans-serif;
    text-align: center;
    letter-spacing: 1px;
    font-size: 1rem;
    font-weight: 700;
    animation: box-animate 3s linear  infinite  ;
    background-image: url(./image/iconmonstr-lock-18-240.png) ;
    background-position: center;
    background-size: 2rem;
    background-repeat: no-repeat;
}
#btn:hover {
    background-image: url(./image/iconmonstr-lock-16-240.png);
    background-size: 3rem;
    top: 49.5vh;
}


@keyframes box-animate {
    0% {
        box-shadow: 0px 4px 2px blue;
    }
    25% {
        box-shadow: -4px 0px 2px blue;
    }
    50% {
        box-shadow: 0px -4px 2px blue;
    }
    75% {
        box-shadow: 4px 0px 2px blue;
    }
    100% {
        box-shadow: 0px 4px 2px blue;
    }
}