Option to customise the overlay

[Xelazu]

Right now there is no option to customize the overlay. It only contains its default colors which are white and pink. It would be nice if we have an options where we can change the colors for something else or have like a configuration file where we can customize the CSS.

[ChillarAnand]

The current overlay is not that visible on the light theme or light background. So, if we have an option to customize, that would be great.