[omnibox chrome:omnibox] Adjust styling.

The previous CL crrev.com/c/1382899 updated the styling of the inputs section.
This CL follows up with additional minor styling changes:
1) Adds light gray background to hovered checkboxes. The previous CL added
similar backgrounds to the other elements (text inputs, selects, buttons).
2) Synchronizes the heights of input elements. Most of the input elements had
similar heights (20-26px), except the checkboxes, which were noticeably smaller.
This CL gives all the input elements 26px heights.
3) Adjusts colors and border thicknesses.
4) Adjusts table vertical spacing. Previously, there was no spacing between
the input and outputs sections unless table details were shown.
5) Styles the table details section.

Bug: 891303
Change-Id: Ifca41272aff09a6cafc369c32e82c749b4436b9f
Reviewed-on: https://chromium-review.googlesource.com/c/1391308
Commit-Queue: manuk hovanesian <manukh@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620529}
5 files changed