html{
    height: 100%;
}
*{
    margin: 0;
    padding: 0;
}
body{
    box-sizing: border-box;
    font-family: sans-serif;
    background: linear-gradient(#141e30, #243b55);
}
.login-box{
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%,-50%);
    width: 400px;
    padding: 40px;
    background-color: rgba(0, 0, 0, 0.5);
    background-repeat: no-repeat;
    box-sizing: border-box;
    border-radius: 10px;
}
.login-box h2{
    color: #fff;
    margin: 0 0 30px 0;
    padding: 0;
    text-align: center;
}
.login-box .user-box{
    position: relative;
}
.login-box .user-box input{
    width: 100%;
    padding: 10px 0;
    font-size: 16px;
    color: #fff;
    margin-bottom: 30px;
    border: none;
    background: transparent;
    border-bottom: 1px solid #fff;
    outline: none;
}
.login-box .user-box label {
    position: absolute;
    color: #fff;
    top: 0;
    left: 0;
    padding: 10px 0;
    font-size: 16px;
    pointer-events: none;

}
.login-box .user-box span{
    position: absolute;
    color: red;
    left: 0;
    top: 65%;
    font-size: 12px;
}
.login-box .user-box input.err{
    border-bottom: 1px solid #f00;
}
.login-box .user-box input.valid{
    border-bottom: 1px solid #0f0;
}

.login-box .user-box input:focus ~ label,
.login-box .user-box input:valid ~ label{
    top: -20px;
    left: 0;
    color: #03e9f4;
    font-size: 12px;
}
.login-box form a{
    position: absolute;
    display: flex;
    top: 420px;
    left: 150px;
}
#btn{
    width: 100%;
    padding: 10px;
    background-color: blue;
    color: #fff;
    border: none;
    outline: none;
    border-radius: 5px;
    cursor: pointer;
}