According to the site you indicated, they just made an image with two desired images.
And in hover mode, they just change the back position.
Example:
.srss{ background-image:url(images/rss-icon.png); background-position:bottom; } .srss:hover{ background-position:top; }
With HTML according to this:
Using an image like this
<a href="http://lalomacd.com.mx/2013/feed/" target="blank"><img class="srss" src="http://lalomacd.com.mx/2013/wp-content/themes/laloma-theme-second/images/blank.png" alt=""></a>
All this can be obtained directly from the site viewing the source and css
Of course, this is not the only way, you can change the background image instead of the background position, but all this corresponds to the way you like it most
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