Form contact avec validation en css

<!DOCTYPE html>
<html>
<head>
    <title>FORM CONTACT AVEC VALIDATION en CSS | Par NGLESSON</title>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <meta name="author" content="Mezgani said">
    <meta name="copyright" content="NGLESSON">
    <link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css"> 
    <link href="style.css" rel="stylesheet" type="text/css">	
</head>
<body class="container">
    <div class="row mt-5">
        <form class="contact_form col-lg-6 col-12" action="#" method="post" name="contact_form">
            <ul>
                <li>
                    <h2>Contact Us</h2>
                    <span class="required_notification">* Required input</span>
                </li>
                <li>
                    <label for="name">Name:</label>
                    <input type="text"  placeholder="Name" required />
                </li>
                <li>
                    <label for="email">Email:</label>
                    <input type="email" name="email" placeholder="Email" email required />
                    <span class="form_hint">Proper format "name@something.com"</span>
                </li>
                <li>
                    <label for="website">Website:</label>
                    <input type="url" name="website" placeholder="Website" required pattern="(http|https)://.+"/>
                    <span class="form_hint">Proper format "https://www.nglesson.com"</span>
                </li>
                <li>
                    <label for="message">Message:</label>
                    <textarea name="message" cols="40" rows="6" required ></textarea>
                </li>
                <li>
                    <button class="submit" type="submit">Submit Form</button>
                </li>
            </ul>
        </form>
    </div>
</body>
</html>
/* === Remove input autofocus webkit === */
*:focus {outline: none;}

/* === Form Typography === */
body {font: 14px/21px "Lucida Sans", "Lucida Grande", "Lucida Sans Unicode", sans-serif;}
.contact_form h2, .contact_form label {font-family:Georgia, Times, "Times New Roman", serif;}
.form_hint, .required_notification {font-size: 11px;}

/* === List Styles === */
.contact_form ul {
    width:750px;
    list-style-type:none;
	list-style-position:outside;
	margin:0px;
	padding:0px;
}
.contact_form li{
	padding:12px; 
	border-bottom:1px solid #eee;
	position:relative;
} 
.contact_form li:first-child, .contact_form li:last-child {
	border-bottom:1px solid #777;
}

/* === Form Header === */
.contact_form h2 {
	margin:0;
	display: inline;
}
.required_notification {
	color:#d45252; 
	margin:5px 0 0 0; 
	display:inline;
	float:right;
}

/* === Form Elements === */
.contact_form label {
	width:150px;
	margin-top: 3px;
	display:inline-block;
	float:left;
	padding:3px;
}
.contact_form input {
	height:40px; 
	width:220px; 
	padding:5px 8px;
}
.contact_form textarea {padding:8px; width:300px;}
.contact_form button {margin-left:156px;}

	/* form element visual styles */
	.contact_form input, .contact_form textarea { 
		border:1px solid #aaa;
		box-shadow: 0px 0px 3px #ccc, 0 10px 15px #eee inset;
		border-radius:2px;
		padding-right:30px;
		-moz-transition: padding .25s; 
		-webkit-transition: padding .25s; 
		-o-transition: padding .25s;
		transition: padding .25s;
	}
	.contact_form input:focus, .contact_form textarea:focus {
		background: #fff; 
		border:1px solid #555; 
		box-shadow: 0 0 3px #aaa; 
		padding-right:70px;
	}

/* === HTML5 validation styles === */	
.contact_form input:required, .contact_form textarea:required {
	background: #fff url(red_asterisk.png) no-repeat 98% center;
}
.contact_form input:required:valid, .contact_form textarea:required:valid {
	background: #fff url(valid.png) no-repeat 98% center;
	box-shadow: 0 0 5px #5cd053;
	border-color: #28921f;
}
.contact_form input:focus:invalid, .contact_form textarea:focus:invalid {
	background: #fff url(invalid.png) no-repeat 98% center;
	box-shadow: 0 0 5px #d45252;
	border-color: #b03535
}

/* === Form hints === */
.form_hint {
	background: #d45252;
	border-radius: 3px 3px 3px 3px;
	color: white;
	margin-left:8px;
	padding: 1px 6px;
	z-index: 999; /* hints stay above all other elements */
	position: absolute; /* allows proper formatting if hint is two lines */
	display: none;
}
.form_hint::before {
	content: "\25C0";
	color:#d45252;
	position: absolute;
	top:1px;
	left:-6px;
}
.contact_form input:focus + .form_hint {display: inline;}
.contact_form input:required:valid + .form_hint {background: #28921f;}
.contact_form input:required:valid + .form_hint::before {color:#28921f;}
	
/* === Button Style === */
button.submit {
	background-color: #68b12f;
	background: -webkit-gradient(linear, left top, left bottom, from(#68b12f), to(#50911e));
	background: -webkit-linear-gradient(top, #68b12f, #50911e);
	background: -moz-linear-gradient(top, #68b12f, #50911e);
	background: -ms-linear-gradient(top, #68b12f, #50911e);
	background: -o-linear-gradient(top, #68b12f, #50911e);
	background: linear-gradient(top, #68b12f, #50911e);
	border: 1px solid #509111;
	border-bottom: 1px solid #5b992b;
	border-radius: 3px;
	-webkit-border-radius: 3px;
	-moz-border-radius: 3px;
	-ms-border-radius: 3px;
	-o-border-radius: 3px;
	box-shadow: inset 0 1px 0 0 #9fd574;
	-webkit-box-shadow: 0 1px 0 0 #9fd574 inset ;
	-moz-box-shadow: 0 1px 0 0 #9fd574 inset;
	-ms-box-shadow: 0 1px 0 0 #9fd574 inset;
	-o-box-shadow: 0 1px 0 0 #9fd574 inset;
	color: white;
	font-weight: bold;
	padding: 6px 20px;
	text-align: center;
	text-shadow: 0 -1px 0 #396715;
}
button.submit:hover {
	opacity:.85;
	cursor: pointer; 
}
button.submit:active {
	border: 1px solid #20911e;
	box-shadow: 0 0 10px 5px #356b0b inset; 
	-webkit-box-shadow:0 0 10px 5px #356b0b inset ;
	-moz-box-shadow: 0 0 10px 5px #356b0b inset;
	-ms-box-shadow: 0 0 10px 5px #356b0b inset;
	-o-box-shadow: 0 0 10px 5px #356b0b inset;
	
}