On 1/4/23 10:25, Ray Andrews via Users wrote:
On 2023-01-03 17:23, bork via Users wrote:

notebook > header.top > tabs > tab:hover:not(:checked), notebook > 
header.top > tabs > tab:checked {
    border-top-width: 3px;
    border-top-color: #FC7BF4; /*test- pink top border. Change as 
desired. */
    margin-top: 0;
    padding-top: 1px; }

I cut and pasted that into new file: /root/.config/geany/geany.css and I 
get this msg:

(geany:3288): Geany-WARNING **: 08:20:34.428: Failed to load custom CSS: 
geany.css:1:0Expected a valid selector
I think you misunderstood or I wasn't clear 'nuf.
(In Linux), the geany.css file - PROBABLY located /usr/share/geany/geany.css.

Normally, & esp. for "non-expert" coders (I am not), not a good idea to edit root owned files. WHEN possible, copy the file into the user home directory (~/).  But not executable or library files, etc.
In your user home dir, you don't (& should NOT) be using "root-anything" - in code, as a gen. rule.

In Linux, the "~/.config" folder is used by many apps to place their "config" files.  They may be conf, config, xml or other.

Just go to ~/.config.  See if a geany folder exists.
If not, create it so path is: ~/.config/geany/.
Then Right click & COPY (don't try to cut / paste) the geany.css file FROM: /usr/share/geany/ into .config, so it looks: .config/geany/geany.css.

Once it's copied to user's home dir, it's no longer root owned.  Since CSS isn't a core file or executable, that's not a security issue.  But editing root owned files in root owned directories CAN be security risk, depending.
 
Once it's in /home/user-name/.config/geany/, the geany.css file will override the one in /usr/share/. Then WITHOUT adding any "/root/" part, just paste the code, just as I listed, at the bottom of the geany.css file you just copied, then save.

You'll have to restart geany - if running, for code to change.  If that doesn't work, open the Settings app, that contains Themes or Appearance (depending on the distro).
Select a different theme - it needs to be a theme from the "Controls" section of themes (not a panel/ desktop, or window borders / title, or mouse theme, etc.).

Then switch right back to the theme you had - that makes lots of apps start using the changed code that affects UI.

  You can also copy entire Linux themes from root owned locations the same way, into ~/.themes.  Rename the copied theme's main folder, to like "my-mint-x-aqua" or such, so you can tell (in Settings > Themes) which ones are in your home/.themes location & you edited them. It's MUCH better than trying to edit themes in root-owned location- & screwing something up.

Then edit the hell out of them in ~/.themes.  If it totally screws up, just delete it from the /home/.themes folder & start over.