style.css

*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
html{
    scroll-behavior: smooth;
    overflow-x: hidden;
    user-select: none;
}
body{
    width: 100vw;
    height: 100vh;
    background-color: rgba(94, 92, 92, 0.212);
}

form{
    width:25rem;
    height: 30rem;
    background-color: white;
    border: 1px solid lightgray;
    border-radius: 15px;
    display: flex;
    flex-flow: column nowrap;
    justify-content: center;
    align-items: center;
    gap:2rem;
    overflow: hidden;
}
h3{
    text-align: center;
    font-size: 2rem;
    color:teal;
}
input{
    outline: none;
    background: rgba(166, 240, 240, 0.103);
    width: 60%;
    font-size: 0.9rem;
    caret-color: tomato;
    padding: 0.5rem;
    border: 1px solid rgba(40, 131, 131, 0.377);
    border-radius: 5px;
    font-weight: 500;
}

input:focus{
    color: teal;
    border-color:teal;
}
button{
    padding: 0.7rem;
    width: 60%;
    border: none;
    outline: none;
    background: tomato;
    color: white;
    border-radius: 5px;
    cursor: pointer;
}

p{
    color: gray;
}
a{
    color: tomato;
}
input:invalid{
    border-color: brown;
    color: brown;
}
.container{
    height: 100%;
    width: 100%;
    display: grid;
    place-items: center;
    position: relative;
}
#sign-in,#sign-up{
    position: absolute;
}
.active{
    transform: rotate(-5deg);
    z-index: 0;

}
div:not(.active){
    transform: rotate(0);
    z-index: 1;
    animation: moving .3s ease-in-out;
}



@keyframes moving{
    from{
        transform:perspective(200px) rotateY(180deg);
    }
    to{
        transform:perspective(200px) rotate(0); 
    }
}