File: style.css

body {
    font-size: 0.9em;
    color: #212121;
    font-family: Arial;
}
.container{
	width: 350px;
    margin: 50px auto;
    box-sizing: border-box;
}

#frm-mobile-verification {
    border: #E0E0E0 1px solid;
    border-radius: 3px;
    padding: 30px;
    text-align: center;
}

.form-heading {
    font-size: 1.5em;
    margin-bottom: 30px;
}

.form-row {
    margin-bottom: 30px;
}

.form-input {
    padding: 10px 20px;
    width: 100%;
    box-sizing: border-box;
    border-radius: 3px;
    border: #E0E0E0 1px solid;
}

.btnSubmit {
    background: #4cb7ff;
    padding: 8px 20px;
    border: #47abef 1px solid;
    border-radius: 3px;
    width: 100%;
    color: #FFF;
}


.error {
    color: #483333;
    padding: 10px;
    background: #ffbcbc;
    border: #efb0b0 1px solid;
    border-radius: 3px;
    margin: 0 auto;
    margin-bottom: 20px;
    width: 350px;
    display:none;
    box-sizing: border-box;
}

.success {
    color: #483333;
    padding: 10px 20px;
    background: #cff9b5;
    border: #bce4a3 1px solid;
    border-radius: 3px;
    margin: 0 auto;
    margin-bottom: 20px;
    width: 350px;
    display:none;
    box-sizing: border-box;
}

.btnVerify {
    background: #4CAF50;
    padding: 8px 20px;
    border: #449e48 1px solid;
    border-radius: 3px;
    width: 100%;
    color: #FFF;
}