I want to create a theme where many UI elements can be customized. Like accent line of active tab, color of background/active tabs etc. I tried submitting a lightweight theme. However, the only thing that can be done there is just submit a background image, select tab color and text color.
Then I came across this theme https://addons.mozilla.org/en-US/firefox/addon/solarized-fox/. Notice the orange active tab line color. How is this done in a lightweight theme? Please help.