Questions[syntax-highlighting](ubuntu)

I've been learning some HTML code recently, and something weird is up with Gedit's highlighting. Whenever I try to use the <h3> tag, Gedit immediately cancels all the highlighting and the text becomes plain white. If I leave and come back, the problem persists. The only way to get the highlighting back is to restore and earlier version of the file by not saving or to start all over again. Does anyone know what's going on?

Extra details:

OS: Ubuntu 20.04

Gedit Version: 3.36.2

Gedit Color Scheme: Cobalt

Screenshots:

Pre-pressing enter (look at the tag)

Post-pressing enter

Background: To enable Nano's syntax highlighting I have configured various shared .nanorc files with the format /usr/share/nano/*.nanorc, eg /usr/share/nano/python.nanorc

This works well but I keep running into issues with Python where I would like it to convert tabs to spaces.

That setting is available (How do I get spaces instead of tabs in nano?) with set tabstospaces, but it seems it has to be global.

Q. Is there a way to have this setting apply only on Python files?

I tried to move set tabstospaces to the relevant nanorc file, python.nanorc mentioned above. However when I try this I get an error upon saving the file in Nano indicating that I can't do this because included files cannot contain set:

Error in /usr/share/nano/python.nanorc on line 42: Command "set" not allowed in included file

Perhaps this is simply a nano limitation and I have to set it only at the global level, but it would be ideal if it could be per syntax. It's not the biggest disaster as Nano is not my main text editor for code but it often convenient for something small.

I am currently trying out KDevelop 5.2.1 for a C++ project on Ubuntu 18 and so far, everything is working as expected, except syntax coloring. I have not been able to personalize it the way I want. What I am doing is the following:

1. Settings -> Configure KDevelop... -> Editor -> Fonts & Colors
2. New Schema
3. There I change the colors, default text styles and Highlight text style (for C++)

When I change colors there, some have the wanted effect (ex.: backgroung) but others seem to have no effect (ex.: macros). For example, for a custom macro function, I have not been able so far to change from the blue/greeninsh default coloring. Same for custom types or variables (which seem to be randomly colored).

In Highlighting Text Style, I have tried setting everything to white and to my surprise, most of the code is still colored (I was looking at a .cpp file).

Is there something I am doing wrong? How can I change these colors?

How to configure VIM to be able to highlight scala language (.scala files extension)?

Current VIM configuration (.vimrc file): :syntax on

I found pygmentize thanks to this answer, but it would be great if it could be used to highlight text with less or maybe replace the command.
Is there a way to do that? Thanks in advance.