<div class="wrapper">
	<div class="container">
		<h1>Welcome</h1>
		
		<form class="form">
			<input type="text" placeholder="Username">
			<input type="password" placeholder="Password">
			<button type="submit" id="login-button">Login</button>
		</form>
	</div>
	
	<ul class="bg-bubbles">
		<li></li>
		<li></li>
		<li></li>
		<li></li>
		<li></li>
		<li></li>
		<li></li>
		<li></li>
		<li></li>
		<li></li>
	</ul>
</div>
@import url(https://fonts.googleapis.com/css?family=Source+Sans+Pro:200,300);

@prim: #53e3a6;

*{
	box-sizing: border-box;
	margin: 0;
	padding: 0;
	
	font-weight: 300;
}

body{
	font-family: 'Source Sans Pro', sans-serif;
	color: white;
	font-weight: 300;
	
	::-webkit-input-placeholder { /* WebKit browsers */
		font-family: 'Source Sans Pro', sans-serif;
			color:    white;
		font-weight: 300;
	}
	:-moz-placeholder { /* Mozilla Firefox 4 to 18 */
		font-family: 'Source Sans Pro', sans-serif;
		 color:    white;
		 opacity:  1;
		font-weight: 300;
	}
	::-moz-placeholder { /* Mozilla Firefox 19+ */
		font-family: 'Source Sans Pro', sans-serif;
		 color:    white;
		 opacity:  1;
		font-weight: 300;
	}
	:-ms-input-placeholder { /* Internet Explorer 10+ */
		font-family: 'Source Sans Pro', sans-serif;
		 color:    white;
		font-weight: 300;
	}
}

.wrapper{
	background: #50a3a2;
background: -webkit-linear-gradient(top left, #50a3a2 0%, #53e3a6 100%);
background: -moz-linear-gradient(top left, #50a3a2 0%, #53e3a6 100%);
background: -o-linear-gradient(top left, #50a3a2 0%, #53e3a6 100%);
background: linear-gradient(to bottom right, #50a3a2 0%, #53e3a6 100%);
	
	position: absolute;
	top: 50%;
	left: 0;
	width: 100%;
	height: 400px;
	margin-top: -200px;
	overflow: hidden;
	
	&.form-success{
		.container{
			h1{
				transform: translateY(85px);
			}
		}
	}
}

.container{
	max-width: 600px;
	margin: 0 auto;
	padding: 80px 0;
	height: 400px;
	text-align: center;
	
	h1{
		font-size: 40px;
		transition-duration: 1s;
		transition-timing-function: ease-in-put;
		font-weight: 200;
	}
}

form{
	padding: 20px 0;
	position: relative;
	z-index: 2;
	
	input{
		display: block;
		appearance: none;
		outline: 0;
		border: 1px solid fade(white, 40%);
		background-color: fade(white, 20%);
		width: 250px;
		
		border-radius: 3px;
		padding: 10px 15px;
		margin: 0 auto 10px auto;
		display: block;
		text-align: center;
		font-size: 18px;
		
		color: white;
		
		transition-duration: 0.25s;
		font-weight: 300;
		
		&:hover{
			background-color: fade(white, 40%);
		}
		
		&:focus{
			background-color: white;
			width: 300px;
			
			color: @prim;
		}
	}
	
	button{
		appearance: none;
		outline: 0;
		background-color: white;
		border: 0;
		padding: 10px 15px;
		color: @prim;
		border-radius: 3px;
		width: 250px;
		cursor: pointer;
		font-size: 18px;
		transition-duration: 0.25s;
		
		&:hover{
			background-color: rgb(245, 247, 249);
		}
	}
}

.bg-bubbles{
	position: absolute;
	top: 0;
	left: 0;
	width: 100%;
	height: 100%;
	
	z-index: 1;
	
	li{
		position: absolute;
		list-style: none;
		display: block;
		width: 40px;
		height: 40px;
		background-color: fade(white, 15%);
		bottom: -160px;
		
		-webkit-animation: square 25s infinite;
		animation:         square 25s infinite;
		
		-webkit-transition-timing-function: linear;
		transition-timing-function: linear;
		
		&:nth-child(1){
			left: 10%;
		}
		
		&:nth-child(2){
			left: 20%;
			
			width: 80px;
			height: 80px;
			
			animation-delay: 2s;
			animation-duration: 17s;
		}
		
		&:nth-child(3){
			left: 25%;
			animation-delay: 4s;
		}
		
		&:nth-child(4){
			left: 40%;
			width: 60px;
			height: 60px;
			
			animation-duration: 22s;
			
			background-color: fade(white, 25%);
		}
		
		&:nth-child(5){
			left: 70%;
		}
		
		&:nth-child(6){
			left: 80%;
			width: 120px;
			height: 120px;
			
			animation-delay: 3s;
			background-color: fade(white, 20%);
		}
		
		&:nth-child(7){
			left: 32%;
			width: 160px;
			height: 160px;
			
			animation-delay: 7s;
		}
		
		&:nth-child(8){
			left: 55%;
			width: 20px;
			height: 20px;
			
			animation-delay: 15s;
			animation-duration: 40s;
		}
		
		&:nth-child(9){
			left: 25%;
			width: 10px;
			height: 10px;
			
			animation-delay: 2s;
			animation-duration: 40s;
			background-color: fade(white, 30%);
		}
		
		&:nth-child(10){
			left: 90%;
			width: 160px;
			height: 160px;
			
			animation-delay: 11s;
		}
	}
}

@-webkit-keyframes square {
  0%   { transform: translateY(0); }
  100% { transform: translateY(-700px) rotate(600deg); }
}
@keyframes square {
  0%   { transform: translateY(0); }
  100% { transform: translateY(-700px) rotate(600deg); }
}
View Compiled
 $("#login-button").click(function(event){
		 event.preventDefault();
	 
	 $('form').fadeOut(500);
	 $('.wrapper').addClass('form-success');
});

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js