As we know kde plasma have default theme called Breeze which has all theme component like look and feel,Desktop theme,Splash screen,colors,icon,widget style,window decoration.etc.
So my question is,how do i customize all breeze theme and where do i get the source code.

This should help you - https://userbase.kde.org/Plasma/Create_ ... el_Package

johnpaulding wrote:This should help you - https://userbase.kde.org/Plasma/Create_ ... el_Package

Thank you for this.
But how do i make widget style that can be seen in application style/widget style?

https://techbase.kde.org/Development/Tutorials/Plasma5

The last one might help; The Plasma Theme Structure in Detail https://techbase.kde.org/Development/Tu ... emeDetails

viewtopic.php?f=17&t=142362&p=382368&hilit=documentation#p382368

Application Style != Desktop Style.
Application styles are mainly written in C++, and there are only a couple of styles (or style engines) currently available for Qt5.
Destkop styles are mainly written in qml, and there are many styles available on the kde store.

For Application Style, I'd suggest starting by taking a look at Kvantum: https://store.kde.org/p/1005410/. This is a highly customizable theme engine that uses svgs for most of the elements. Kvantum themes have their own category in the kde store.

If you are more interested in writing your own style in c++, the source for the Breeze theme is available at https://cgit.kde.org/breeze.git (mirrored on github at https://github.com/KDE/breeze).