First off, when you have to out a class on every single element (such as every single anchor) then you know that you’re doing something wrong.
What you’re doing there can be easily done without using any classes on the links at all.
Set the anchor display to inline-block instead of block, because you want to affect their width and height but also keep them in the same line.
Remove the negative margin from those anchors, just remove the margin itself.
And remove the CSS a.x1 through to a.x5 styles
It all looks good after that tidy up, and the class names can be removed from those links.
Like leaving stuff scattered all over the floor, it becomes a detrimental distraction and needs to be cleaned up.
The center spot is where you can place another link with a class name, that gives it a white background instead of green, and gives you the good ability to put the play pause controls. "controls" seems like a good name for that class, until something better comes to mind.