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CSS

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HTML 

              
                <!-- form -->
<div class="form-box">
	
	<!-- tab -->
	<ul class="tab-group">
		<li class="tab active"><a href="#signup">Sign Up</a></li>
		<li class="tab"><a href="#login">Log In</a></li>
	</ul>
	<!-- //tab -->
	
	<!-- tab-cotent -->
	<div class="tab-content">
		<!-- Sign Up for Free -->
		<div id="signup">
			<h1>Sign Up for Free</h1>
			
			<form action="/" method="post">
				
				<div class="top-row">
					<div class="field-wrap">
						<label for="first-name">
							First Name <span class="req">*</span>
						</label>
						<input type="text" id="first-name" required autocomplete="off">
					</div>
					
					<div class="field-wrap">
						<label for="last-name">Last Name <span class="req">*</span></label>
						<input type="text" id="last-name" required autocomplete="off">
					</div>
				</div>
				
				<div class="field-wrap">
					<label for="email">
						Email Address <span class="req">*</span>
					</label>
					<input type="email" id="email" required autocomplete="off">
				</div>
				
				<div class="field-wrap">
					<label for="pwd">
						Set A Password <span class="req">*</span>
					</label>
					<input type="password" id="pwd" required autocomplete="off">
				</div>
				
				<button type="submit" class="button button-block">Get Started</button>
				
			</form>
			
		</div>
		<!-- // Sign Up for Free -->
		
		<!-- Welcome Back! -->
		<div id="login">
			<h1>Welcome Back!</h1>
			
			<form action="/" method="post">
				
				<div class="field-wrap">
					<label for="email2">
						Email Address <span class="req">*</span>
					</label>
					<input type="text" id="email2" required autocomplete="off">
				</div>
				
				<div class="field-wrap">
					<label for="pwd2">
						Password <span class="req">*</span>
					</label>
					<input type="text" id="pwd2" required autocomplete="off">
				</div>
				
				<p class="forgot"><a href="#">Forgot Password?</a></p>
				
				<button type="submit" class="button button-block">Log In</button>
				
			</form>
			
		</div>
		<!-- Welcome Back! -->
		
	</div>
	<!-- //tab-cotent -->
	
</div>
<!--  // form -->
!

CSS 

              
                *, *:before, *:after {
	margin: 0;
	padding: 0;
	box-sizing: border-box;
}
html {
	overflow-y: scroll;
}
body {
	background: #c1bdba;
	font-family:sans-serif;
}
a {
	text-decoration: none;
	color: #1ab188;
	-webkit-transition: .5s ease;
	transition: .5s ease;
}
li {
	list-style:none;
}
a:hover {
	color: #179b77;
}

.form-box {
	background: rgba(19,35,47, .9);
	padding: 40px;
	max-width: 600px;
	margin: 40px auto;
	border-radius: 4px;
	box-shadow: 0 4px 10px 4px rgba(9,35,47, .5)
}

.tab-group {
	margin: 0 0 40px 0;
}
.tab-group::after {
	content: "";
	display: table;
	clear: both;
}
.tab-group li a {
	display: block;
	padding: 15px;
	font-size: 20px;
	float: left;
	width: 50%;
	text-align: center;
	/* 전이기 일어나기 전의 초기 스타일 */
	background: rgba(160, 179, 176, .25);
	color: #a0b3b0;
	/* 초기 스타일에 화면 전이를 설정 */
	-webkit-transition: .5s ease;
	transition: .5s ease;
}
.tab-group li a:hover {
	/* 마우스오버를 할 경우에 나타나는 전이에 대한 스타일을 정의 */
	background-color: #179b77;
	color: #fff;
}
.tab-group .active a {
	background: #1ab188;
	color: #fff;
}
.tab-content > div:last-child {
	display: none;
}
h1 {
	text-align: center;
	color: #fff;
	font-weight: 300;
	margin-bottom: 40px;
}
label {
	pointer-events: none;
	position: absolute;
	left:13px;
	/* 화면 전이가 일어나기 전의 스타일 정의 */
	/* 레이블 위치 스타일 정의 */
	-webkit-transform: translateY(6px);
	transform: translateY(6px);
	color: rgba(255, 255, 255, .5);
	font-size: 22px;
	/* 화면 전이 정의 */
	-webkit-transition: all 0.25s ease;
	transition: all 0.25s ease;
}
label .req {
	margin: 2px;
	color: #1ab188;
}
label.active {
	/* 화면 전이의 최종 변천 스타일 정의 */
	-webkit-transform: translateY(50px);
	transform: translateY(50px);
	left: 2px;
	font-size: 14px;
}
label.active .req {
	opacity: 0;
}
label.highlight {
	color: #ffffff;
}
input, textarea {
	font-size: 22px;
	display: block;
	width: 100%;
	height: 100%;
	padding: 5px 10px;
	background: none; /* 밑 배경색 보여주기 위해 none 처리 */
	border: 1px solid #a0b3b0;
	color: #fff;
	border-radius: 0;
	-webkit-transition: border-color .25s ease, box-shadow .25s ease;
	transition: border-color .25s ease, box-shadow .25s ease;
}
input:focus, textarea:focus {
	outline: 0;
	border-color: #1ab188;
}
textarea {
	border: 2px solid #a0b3b0;
	resize: vertical;
}
.field-wrap {
	position: relative;
	margin-bottom: 40px;
}
.top-row::after {
	display: table;
	clear: both;
	content: "";
}
.top-row > div {
	float: left;
	width: 48%;
	margin-right: 4%;
}
.top-row > div:last-child {
	margin: 0;
}
.button {
	padding: 15px 0;
	border: 0;
	outline: none;
	border-radius: 0;
	font-size: 2rem;
	font-weight: 600;
	text-transform: uppercase;
	letter-spacing: .1em;
	background: #1ab188;
	color: #fff;
	-webkit-appearance: none;
	-webkit-transition: all 0.5s ease;
	transition: all 0.5s ease;
}
.button:hover, .button:focus {
	background: #179b77;
}
.button-block {
	display: block;
	width: 100%;
}
.forgot {
	margin: -20px 0 20px;
	text-align: right;
}
!

JS 

              
                var formTarget = $('.form-box').find('input, textarea');
formTarget.on('keyup blur focus', function (e) {
	
	var $this = $(this),
		label = $this.prev('label');
	
	if (e.type === 'keyup') {
		if ($this.val() === '') {
			label.removeClass('active highlight');
		} else {
			label.addClass('active highlight');
		}
	} else if (e.type === 'blur') {
		if( $this.val() === '' ) {
			label.removeClass('active highlight');
		} else {
			label.removeClass('highlight');
		}
	} else if (e.type === 'focus') {
		
		if( $this.val() === '' ) {
			label.removeClass('highlight');
		}
		else if( $this.val() !== '' ) {
			label.addClass('highlight');
		}
	}
	
});

var tab = $('.tab a');
tab.on('click', function (e) {
	
	e.preventDefault();
	
	$(this).parent().addClass('active');
	$(this).parent().siblings().removeClass('active');
	
	var target = $(this).attr('href'),
		tabContents = $('.tab-content > div');
	
	tabContents.not(target).hide();
	
	$(target).fadeIn(600);
	
});
!
999px

Console