Move Visualization/Data selector on top of visualization

I noticed that the buttons were hard to push when testing
the tool on a mobile phone were graphics tend to overlap.
I moved the buttons after the graphics in the DOM, to ensure
that they be displayed on top.
Restore background of button to transparent, not white

The buttons for the selection of Visualization / Raw Data
used to display on a white background, hiding the underlying
visualization in case of overlap. I restored the default
background color instead, transparent.