I have downloaded the latest version(2.1) of qupzilla as an appimage from here and its working fine. I want to change the default theme to this. I have downloaded the files in a folder called cyano. Now how should I add this theme to qupzilla?
First I tried to find qupzilla folder inside /usr/share/ but there is no such folder in my computer
Second I created a themes folder inside /home/me/.config/qupzilla/profiles/default/ and copy paste cyano folder to it
But both didn't worked.
In order to install a new theme in Qupzilla (including for an appimage) you have to put it in ~/.config/qupzilla/themes/.
It seems the theme you mentioned is not available at the same link anymore and there are not many others available. I have found this one and tested for the purpose of this answer, although it is almost identical to the default Linux theme.
Some notes on Qupzilla an its looks:
Properly installed (that is: not just as an appimage) it has great integration with the desktop theme. I was able to see that with the Ubuntu repo version 1.8.9 in Plasma 5.
I am not able to find a way to install later versions, only appimages seem available and they do not have that great theming integration, hence the need for themes. Here they are: https://github.com/QupZilla/qupzilla/wiki/Themes.
2.2.5 is the latest version. After that it will change name to Falkon.