Do we have to learn everything from existing plugin/theme downloadable??

It's pretty typical to learn from existing plugins/themes. Personally I picked it up after just spending a bunch of time writing one myself. Then I started to form some opinions about how Elgg could make it better and trying to bake those learnings into subsequent versions.

If you have a good understanding of views, that'll get you 80% of the way there. 

http://learn.elgg.org/en/latest/guides/views.html

Use views to override the CSS views in core and you'll be good to go!

Hi Evan,

Thank you very much for an update!

OK, I'll try to understand basics of Elgg views until I become comfortable with them. :)

Thanks again for your help.

Regards,

Sat

or you could download some book's from torrent and start learning :)