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CSS

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HTML 

              
                <section>
	<h1>Two Animated Link Styles</h1>
</section>
<section class="link-style-1">
	<h3>1 - Two Pseudo Elements</h3>
	<p>Lots of fun possibilities, but requires <code>white-space: nowrap;</code> to work correctly. Temporibus ex doloribus iure, <a href="#">dolore quos optio</a> numquam illum, voluptatibus eius delectus laboriosam possimus quia unde suscipit culpa quod minima sint consectetur!</p>
	<p>
		<ul>
			<li class="pro">Uses CSS3 transform property for those sweet gainz.</li>
			<li class="con">Only works with <code>&nbsp;white-space: no-wrap&nbsp;</code>(<em>must</em> be one single line)</li>
		</ul>
	</p>
</section>

<section class="link-style-2">
	<h3>2 - Animated Background Image</h3>
<p>This way is great. The only limitations are that we are animating the background position only and that this does not use CSS3 transform. Temporibus ex doloribus iure, <a href="#">dolore quos optio</a> numquam illum, <a href="#">even long links OK -> laboriosam possimus quia unde suscipit culpa quod minima sint consectetur!</a></p>
	<p>
		<ul>
			<li class="pro">Works on links that wrap across multiple lines.</li>
			<li class="con">Animates the <code>&nbsp;background-position&nbsp;</code> property, so no sweet GPU love :/</li>
			<li class="con">Relatively limited.</li>
		</ul>
	</p>
</section>
!

CSS 

              
                $link-color: blue;
$linkAnimationSpeed: 0.3s;
$text-color: rgba(0,0,0,0.9);
//Style one
//Psuedoelements for before and after
.link-style-1 {
	a {
		color: $text-color;
		text-decoration: none;
		position: relative;
		white-space: nowrap;
		transition: color $linkAnimationSpeed;
		&:after,
		&:before {
			content: '';
			display: block;
			position: absolute;
			//width:100%;
			left: (-2/16) * 1em;
			right: (-2/16) * 1em;
			z-index: -1;
		}
		&:before {
			background-color: $text-color;
			bottom: (-1/16) * 1em;
			height: 1px;
		}
		&:after {
			background-color: $link-color;
			animation: linkUnderlineOut $linkAnimationSpeed forwards;		
			top:0;
			bottom: 0;
			height: 100%;
			transform-origin: bottom left;
			transform: scaleY(0);
		}
	}

	a:hover {

		color: white;

		&:before {

			background-color: $link-color;

		}

		&:after {

			animation: linkUnderlineIn $linkAnimationSpeed forwards;

		}
	}

	@keyframes linkUnderlineIn {
		0% {
			transform: scaleY(0);
		}
		50% {
			transform: scaleY(1.1);
		}
		63% {
			transform: scaleY(0.9);
		}
		88% {
			transform: scaleY(1.05);
		}
		100% {
			transform: scaleY(1);
		}
	}

	@keyframes linkUnderlineOut {
		0% {
			transform: scaleY(1);
		}
		100% {
			transform: scaleY(0);
		}
	}
}

//Style two
//Animated background image
.link-style-2 {
	a {
		border-bottom: 1px solid $text-color;
		color: $text-color;
		text-decoration: none;
		transition: color $linkAnimationSpeed ease-in-out;
		//transition: background-image $linkAnimationSpeed ease-in-out;
		background-size: 100% 200%;
		background-image: linear-gradient(to top, 
			transparent 0%, 
			transparent 50%,
			$link-color 50%, 
			$link-color 100%);
		background-position: 0 100%;
		will-change: background-position;
		
		&:hover {
			animation: backgroundAnimateIn $linkAnimationSpeed;
			// animation-play-state : running;
			animation-fill-mode: forwards;
		}
	}
}

@keyframes backgroundAnimateIn {
	0% {
		background-position: 0 -100%;
	}
	63% {
		background-position: 0 -95%;		
	}
	86% {
		background-position: 0 2.5%;
	}
	100% {
		color: white;
		background-position: 0 0%;
	}
}

body {
	padding: 2vw;
	margin:0;
}
section {
	margin-right: auto;
	margin-left: auto;
	max-width: 540px;	
}

p {
	line-height: 1.6;
}

ul {
	font-size: 0.8125rem;
	li {
		margin-bottom: 0.75em;
	}
}

code {
	background-color: #363636;
	color: white;
	font-size: 0.8125em;
}
!

JS
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