Support the Firefox DevTools dark theme.

[captainbrosset]

Firefox DevTools supports 2 themes (well 3 if you count the Firebug theme, but it's similar to the light theme).
The extension currently looks good when DevTools is set to the light theme. If you switch DevTools to the dark theme however, then things look pretty bad and some things become harder to read.

[captainbrosset]

Light theme:

Dark theme:

Several issues:

• the tab icon stays black, which means it's not visible anymore
• the toolbar (with the search field) stays white, which means it doesn't go well with the rest of the Dark theme
• the HTML syntax highlight colors don't work well anymore (<, >, = and " are black on black, and other colors aren't contrasted enough)
• the hover background that appears when hovering over results isn't visible anymore.

[captainbrosset]

Looks like there is a web extension API that helps with theme support :

browser.devtools.panels.themeName // theme
// event listener
browser.devtools.panels.onThemeChanged.addListener(theme => {});