CSS3制作的非空验证表单提示效果

/* === List Styles === */
.contact_form ul {
    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:20px; 
	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(images/red_asterisk.png) no-repeat 98% center;
}
.contact_form input:required:valid, .contact_form textarea:required:valid {
	background: #fff url(images/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(images/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;}