I have a Napili community where I am using Standard Tabs component to show different standard and custom lightning component. I want to change the background image every time I clicked on the different tab (Not tab background). One image on one tab. How I can achieve that any guesses?
Each tab has a different class, if you scope your CSS rules properly under community branding, you can easily achieve this.
You can use your browser dev tools to help you figure out the proper css scoping:
If you want to completely change the background of the community based on different tabs you have, you will have to create a custom theme layout in order to be able to interact with the template body and within it use tabsets where you can use the onactive attribute to change the template body programmatically.