fix shields outline being trimmed on Windows/Linux

[cezaraugusto]

address brave/brave-browser#4225

now link https://brave-ui-fjd95tx7r.now.sh/?path=/story/feature-components-shields--enabled

Tabbable elements should have a visible focus on all platforms (win/macos/linux)

Test Plan

1. Go to the link above
2. Click anywhere inside the main view so we can grab its focus
3. Start tabbing elements and ensure element's focus ring is not cut, use space to click "Scripts blocked"
4. Keep tabbing
5. No element should have the focus ring trimmed or cut

[petemill]

Instead of fixing this with some 1px shims, could this be rectified by fixing outline-offset of the toggle focus? I see that the outline-offset is attempted to be set, along with outline-size, but those rules are not actually having an effect. They can be fixed by also applying the rule outline-style: solid.

[cezaraugusto]

closing as shields components are in brave-core now. I plan to retouch this work there soon