Arrows to navigate thru slides

[ERIKA]

I'm currently hand-crafting a professional portfolio site, and im trying to find a good way to make images able to be clicked to expand, and I want the gallery to have arrows to navigate to and from other photos, very simple (or so i thought).
Now the arrows aren't appearing and some of the images don't even click to a full-sized image anymore.
attached are images of the regular page adn then a photo of the gallery (and a crude drawing of how i want the arrows to look)



so the page can be found here, the HTML is here, and the css for the gallery is here. It was working earlier and now there's nothing... help D: