style.css

* {
    margin: 0;
    padding: 0;
}

body {
    background-image: url('xkcd.jpg');
    max-height: 100vh;
    background-repeat: no-repeat;
    box-sizing: border-box;
}

.box {
    top: 50%;
    left: 50%;
    position: absolute;
    transform: translate(-70%, -70%);
    background: #fff;
    padding: 60px 40px;
    width: 400px;
    text-align: center;
    border: 1px solid #000;
}

.box h1 {
    font-size: 36px;
    color: #20D389;
    margin-bottom: 15px;
}

.box span {
    color: #999;
    font-size: 16px;
    text-transform: capitalize;
}

.box input {
    width: 100%;
    box-sizing: border-box;
    padding: 20px;
    border: 1px solid #999;
    border-radius: 5px;
    outline-color: #20D389;
    margin-bottom: 25px;
}

.box button {
    width: 100%;
    padding: 15px 20px;
    border: 0;
    border-radius: 5px;
    background: #20D389;
    color: #fff;
    font-size: 18px;
    font-weight: 700;
    transition: 0.3s;
}

.box hr {
    width 70px;
    color: #999;
    margin: 25px auto;
}

.box button:hover {
    background: #196b49;
}