- Remove duplicated CSS.
- Expand landing area of upload button.
- Give the toolbox a transparent white background.
- Make the phase-select box look nicer before file load.
- Remove the margin at the top of the screen.

The height of the margin was exactly the height of span#graph-toolbox,
and due to the semantics of position:relative, space was reserved for it
at the top of div#middle.

BUG=
R=danno

Review-Url: https://codereview.chromium.org/2164373002
Cr-Commit-Position: refs/heads/master@{#38003}