How to create a hover effect in Alloy UI

AlloyUI is the scripting language build right into liferay that you can use to create fantastic looking responsive UIs that look exactly like liferay´s own portlets. This scripting language is built on top of YUI3 by yahoo. So whenever you don´t find something in AlloyUI´s examples page (http://alloyui.com/), you might want to check YUI´s page (http://yuilibrary.com/).
Today I want to show you a nice fade in / fade out effect that I am using in some of my portlets. As soon as you hover over the "hover-me" div, the "hello world" button will appear. You can use this example directly in liferay : no additional libs needed ! Have fun :)

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If you have any questions, feel free to leave a comment.