* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html, body {
    height: 100%;
    font-family: sans-serif;
    background: #F3F3F3;
    background-position: center center;
    background-size: cover;
    background-repeat: no-repeat;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 20px;
    height: 100vh;
}
.login-box{
    width: 100vw !important;
}
input {
    outline: none;
    border: none;
    background: transparent;
}

.login-box {
    width: 100%;
    max-width: 400px;
    padding: 40px 30px;
    background-color: black;
    box-shadow: 0 15px 25px rgba(0, 0, 0, 0.6);
    border-radius: 10px;
}

    .login-box h2 {
        margin: 0 0 30px;
        color: #fff;
        text-align: center;
    }

.user-box {
    position: relative;
    margin-bottom: 30px;
}

    .user-box input.input {
        width: 100%;
        padding: 10px 0;
        color: #fff;
        border-bottom: 1px solid #fff;
    }

    .user-box label {
        position: absolute;
        top: 0;
        left: 0;
        padding: 10px 0;
        color: #fff;
        transition: 500ms;
        font-size: 16px;
        pointer-events: none;
    }

.input:focus ~ label,
.input:valid ~ label {
    top: -20px;
    color: #b9ff66;
    font-size: 12px;
}

.login-box button {
    display: flex;
    align-items: center;
    justify-content: center;
    background: #b9ff66;
    padding: 15px 30px;
    color: black;
    margin-top: 20px;
    width: 100%;
    border: none;
    cursor: pointer;
    font-size: 15px;
}

@media screen and (max-height: 600px) {
    html, body {
        align-items: flex-start;
    }

    .login-box {
        margin-top: 40px;
        margin-bottom: 40px;
    }
}