I've found this topic on forum related to custom headers: https://community.nodebb.org/topic/2333
But this is a very old topic and plugin cannot be found in plugins page in CMS.
On top of that, as I can see this plugin shows random images for the categories.
So I decided to make my own header. The matter is that I want to have a spefic (responsive) image for an each category (example on the images below). Can you, please, point out what's the most optimal way to create such header? Is it related to theme modification or plugins? Or whatever? I just don't know where to start from.
I use "Persona" theme with "Slate" style. Also I have experience in HTML, CSS, JS & NodeJS, but have zero experience in modyfying NodeBB themes and creating something complex as those headers which I described.
Thanks in advance for any help.
Live code examples and tutorials for beginners will be very helpful.