Remove CSS from background_page.html and change getLinkHintCss to only return the user's overrides.
Add vimiumReset class to html generated by completionDialog, helpDialog, linkHints and vimiumFrontEnd
Add vimium.css to the manifest and link to it in the tests_harnesses/automated.html and options.html.
Add an id, vimiumLinkHintsContainer, to linkhints div to allow user overrides to have a higher specificity.
Change the default for the user CSS override.

Added comments to the linkhints css settings on the options page and set default properties that a user would change to make it clear where they should be modified.
Added a dropshadow to the linkhints to make them stand out better against similarly colored site backgrounds.

Previously, we were taking the dimensions of the dialog while it still
had "display: none;", which caused clientWidth and clientHeight to
return zero.

Problem:
When bookmark completion is aborted using <ESC> key, the
completion dialog is faded out, zero opacity. This leaves
an invisible dialog hovering over the current page's content.
Any thing under the invisible dialog cannot get mouse focus,
including the links.

Solution:
After fading out the dialog, also hide it by its CSS display
property.

Happens when the partial string input matches more results
than can be displayed vertically. This causes the input section
at the top, together with the top matching URLS to disappear.

Solution is to only center the box when it's height is less than
the window height, otherwise it's top is at coordinate 0.
No negative top.