CSS image slider Plugin?

So I am trying to code an image slider that uses no javascript. This is the code I have so far, though it’s just sitting in my front-page.php.

<div id="box">
<ul id="slider">
    <?php
     $counter = 1;
      $thumbnails = get_posts('numberposts=5');
      $permalink = get_permalink($permalink->ID);
      foreach ($thumbnails as $thumbnail) {
         if ( has_post_thumbnail($thumbnail->ID)) {
    ?>
    <li id="<?php echo $counter?>">
    <?php
      echo '<a href="' . get_permalink( $thumbnail->ID ) . '" title="' . esc_attr( $thumbnail->post_title ) . '">';
      echo get_the_post_thumbnail($thumbnail->ID, 'large');
      echo '</a>';
    ?>
      <p><span><a href="<?php echo get_permalink( $thumbnail->ID ) ?>"><?php echo get_the_title($thumbnail) ?></a></span></p>
      </li>
    <?php
          $counter++;
        }
    }
    ?>
</ul>
    <ul id="thumb">
    <?php
        $thumb_counter = 1;
        $thumbs = get_posts('numberposts=5');
        $thumb_permalink = get_permalink($thumb_permalink->ID);
        foreach ($thumbs as $thumb) {
          if ( has_post_thumbnail($thumb->ID)) {
    ?>
        <li><a href="<?php echo '#' . $thumb_counter?>"><?php echo get_the_post_thumbnail($thumb->ID, 'thumbnail');?></a></li>
    <?php
            $thumb_counter++;
          }
      }
    ?>
    </ul>
</div>

CSS:

@-webkit-keyframes fadeIn {
	0% {
		opacity: 0;

	}

	50% {
		opacity: 0;
	}

	100% {
		opacity: 1;
	}
}

#box {
	text-align: left;
	width: 700px;
	margin: 30px auto 0 auto;
	background: #444;
	overflow: hidden;
	border: 10px solid #444;
	-webkit-box-shadow: #131313 0px 2px 10px;
	-moz-box-shadow: #131313 0px 3px 10px;
	box-shadow: #131313 0px 3px 10px;
	-webkit-animation-name: fadeIn;
  	-webkit-animation-duration: 3s;
  	-webkit-animation-iteration-count: 1;
  	-webkit-animation-delay: 0s;
        border-radius: 5px;
}

ul#slider{
	-webkit-border-radius: 10px;
	margin: 0px;
	padding: 0px;
	list-style: none;
	position: relative;
	width: 700px;
	height: 438px;
	overflow: hidden;
}
ul#slider a img{
    width: 100%;
    height: 100%;
    text-align: center;
}

ul#thumb {
	overflow: none;
	margin: 0px 0px 0px 0px;
	padding: 0px;
	list-style: none;
	position: relative;
	overflow: auto;
	width: 700px;
}

ul#thumb a {
	-webkit-transition: opacity .2s ease-in-out;
	border: 1px solid #979797;
	width: 35px;
	height: 35px;
	display: block;
	overflow: hidden;
	float: right;
	margin: 10px 0px 0px 10px;
	opacity: 0.75;
}

ul#thumb a:hover {
	opacity: 1;
} 

ul#slider li {
	width: 700px;
	height: 438px;
	position: absolute;
	}

ul#slider li p {
	position: absolute;
	bottom: 0;
	left: 0;
	z-index: inherit;
	color: #fff;
	background: rgba(0, 0, 0, .5);
	width: 100%;
}

ul#slider li p span {
	line-height: 1.2em;
	padding: 10px;
	display: block;
}

/* Animation for the :target image. Slides the image in. */

@-webkit-keyframes moveTarget {
	0% {
		left:-700px;

	}

	100% {
		left:0px;
	}
}

ul#slider li:target {
	-webkit-animation-name: moveTarget;
	-webkit-animation-duration: .5s;
	-webkit-animation-iteration-count: 1;
	top:0px;
	left: 0px;
	z-index: 10;
}

/*
Animation for the current image. Slides it out the frame and back to the starting position.
Adds a lower z-index than the now current image.
*/

@-webkit-keyframes moveIt {
	0% {
		left:0px;

	}
	50% {
		left:700px;

	}
	100% {
		left:-700px;
		z-index: 5;
	}
}

ul#slider li:not(:target) {
	-webkit-animation-name: moveIt;
  	-webkit-animation-duration: 1.5s;
  	-webkit-animation-iteration-count: 1;
	top:0px;
	left: 0px;
}

I would like to know if it would be smart to make this into a plugin or drop it in the functions file or something like that.

I would also appreciate some feedback on the code, because I am a beginner when it comes to PHP. If you need the entire front-page file, let me know and I’ll put it up.