style.css

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: Verdana, Geneva, Tahoma, sans-serif;
}

body {
    background-color: cornflowerblue;
}

.heading {
    text-align: center;
    margin: 30px 0;
    font-size: 30px;
}

form {
    padding-top: 40px;
    background-color: aliceblue;
    width: 50%;
    height: 500px;
    margin: 30px auto;
}

form .form-group {
    display: flex;
    justify-content: center;
    align-items: center;
}

.form-group input {
    width: 70%;
    padding: 10px;
    margin: 10px 0;
    border: none;
    background-color: transparent;
    border-bottom: 1px solid black;
}

.form-group input:focus {
    outline-color: lightblue;
}

.form-group .sbtn,
.form-group .rbtn {
    margin: 50px 10px;
    cursor: pointer;
    width: 20%;
    padding: 10px;
    font-size: 15px;
    background-color: cornflowerblue;
    border: none;
    border-radius: 10px;
}

.btn:hover {
    border: 2px solid black;
    background-color: white;
}

.fail {
    color: red;
    padding: 5px;
}

.success {
    color: rgb(16, 16, 16);
    padding: 5px;
}

p.error {
    margin-left: 80px;
    font-size: 14px;
}

@media screen and (max-width: 768px) {
    form {
        width: 80%;
        height: auto;
        margin: auto auto;
        padding-top: 30px;
    }
    p.error {
        margin-left: 85px;
        font-size: 13px;
    }
}

@media screen and (max-width: 450px) {
    form {
        padding-top: 20px;
        width: 100%;
        margin: auto 20px 20px auto;
    }
    .form-group .sbtn,
    .form-group .rbtn {
        margin: 50px 10px;
        width: 40%;
        padding: 15px;
    }
    p.error {
        margin-left: 55px;
        font-size: 13px;
    }
}