Stronger focus style for buttons

[simurai]

Prerequisites

• [x] Put an X between the brackets on this line if you have done all of the following:
  • Reproduced the problem in Safe Mode: http://flight-manual.atom.io/hacking-atom/sections/debugging/#using-safe-mode
  • Followed all applicable steps in the debugging guide: http://flight-manual.atom.io/hacking-atom/sections/debugging/
  • Checked the FAQs on the message board for common solutions: https://discuss.atom.io/c/faq
  • Checked that your issue isn't already filed: https://github.com/issues?utf8=✓&q=is%3Aissue+user%3Aatom
  • Checked that there is not already an Atom package that provides the described functionality: https://atom.io/packages

Description

The styling when something is focused is pretty strong for inputs, it adds a blue border around an input. But for buttons it's pretty weak and hard to see.

Steps to Reproduce

1. Open Settings > Install
2. Press cmd to move the focus to "Packages" and "Themes"

Expected behavior:

Buttons should be easy to see when they get focused with the keyboard

Actual behavior:

Buttons are hard to see when they get focused with the keyboard

Reproduces how often:

100%

Versions

You can get this information from copy and pasting the output of atom --version and apm --version from the command line. Also, please include the OS and what version of the OS you're running.

Atom    : 1.16.0-dev-6f9a536
Electron: 1.3.13
Chrome  : 52.0.2743.82
Node    : 6.5.0

Additional Information

The reason for the weak style is that in Chromium, if you click a button with your mouse, it adds the :focus style to that button until you click somewhere else. See this Accessible Styles post for more details.

There is proposal to add a :focusring selector that would allow to have a different style only when focused with the keyboard. But that might still take a while till it's implemented. Other options:

1. Use JS to add some sort of "focused with the keyboard/mouse" class and then style that differently.
2. Make the :focus style stronger, even if it looks too obtrusive.

Let's try option 2 first since that seems simpler. Also, because Atom is an application where the keyboard is used a lot we shouldn't compromise usability for it.