How to change blender User Interface?

Hi I am working on changing blender’s user interface. But there are some doubts.

Like there is a line just above “Render” label, I want to make it in dots.
Thanks in advance

Blenders UI code can be very convoluted C code so I can understand it’s hard to find. In this case the code you are looking for is in C. In the file interface_panel.c and the function ui_draw_aligned_panel. Look for this code:

            glColor4f(0.0f, 0.0f, 0.0f, 0.5f);
            fdrawline(minx, y, maxx, y + 40);
            glColor4f(1.0f, 1.0f, 1.0f, 0.25f);
            fdrawline(minx, y - 1, maxx, y - 1);

Have a look at this site where I was looking into this URL for “How to collapse menus”. I think this may help you check out