For the color theme, I suggest using a light-green coloring with yellowish white background.
On the left hand side of We can put a logo.
###Logo idea
We can use calligraphic writing of the Kalima Tawheed (La-ilaha-illallah..). The writing should be clear enough to be recognized the kaliman, meaning it should not be more art than it's message. I'm against rounding of the writing also. But, A half round circle writing may not be bad.
On top of the Kalima, We can use a palm tree and a crescent on the upper left side of the tree.
###Vote buttons For upvote and downvote icons, I pretty much liked yasar's answer.