Hello, i would be great if Falkon had a dark theme for its entire menus and other windows, think people would love to have this in Falkon .

A couple pieces involved in this:
First is the chrome containing the tabs, url bar, toolbar buttons, etc. This is themed following the Application Style, so selecting a dark Application Style and color scheme should make all of that dark for you.

Second is the html view which is themed following whatever color scheme the web site designers decided to use but usually defaults to black-on-white. I'm not sure what options are available for overriding the color scheme for this part. Other browsers at least allow you to provide a personal CSS file which can be used to override the style provided by the web site. There are also extensions for the other browsers which can invert or customize the style provided by web site. One has to be aware when implementing this functionality of web sites which already use a light-on-dark color scheme that such sites provide a consistent appearance. (I've been using the Midnight Lizard extension for Firefox and it handles this really well)