How to remove stylus-addon styles completely?

Dancer18

I want to have my Telegram web panel in dark-mode. To do this, I first installed an existing chrome extension for it.
This I have deleted later.

Then I found different 'stylus' styles and tried them.

It happened that the fonts suddenly are displayed in Serif.

Even after deleting all styles and cache and restarting, the Serif fonts remain.

How can I change this?

EDIT:// This affects - in general - not only fonts. Also other styles I tried are not all set back to default after deleting the style.
The web panel, for example, no longer shows the mobile version of Telegram, nor can it be changed to that version.

Where can I delete the stylus- remnants? In profile folder of Vivaldi somewhere?

Dancer18

I tried with reinstall of Vivaldi, but it doesn't work. I deinstalled stylus-addon without any effects on this issue.

It is not effected in other profile.
My conclusion:
Somewhere in the profile-folder this style-mod is saved and has to be removed.

But where?

Dancer18

@Gwen-Dragon
I have uninstalled the extension. Then this directory clngdbkpkpeebahjckkjfobafhncgmne is no longer there.
After reinstalling it is there again. Regardless, the Telegram page in Vivaldi without Stylus mods is still with Serif fonts.
Strange.

Dancer18

I could help myself after some research and trying, as a workaround.
How?
I found a style that is

fitting my needs more or less
is easy coded

Then I changed the css-code for color adjustments and for the fonts:

font-family: "Open Sans", "Lucida Grande", "Lucida Sans Unicode", Arial, Helvetica, Verdana, sans-serif !important;

That is working now.

But there is an interesting part left waiting for a solution:

When deactivating the style, the font-family switches to serif again.
And this modification seems to be saved outside from the stylus-extension, but inside Vivaldi profile folder.
As I mentioned before: This is NOT the original font-family of telegram.org.

Any suggestions?

BTW: I made a question at stackoverflow about this issue.

Dancer18

@Gwen-Dragon Thank you for being so helpful.
But it would probably be a coincidence to be able to reproduce this case.

In this respect, my question goes more in these directions:

Who knows a comparable case?
Who knows a delete-command that can be used to undo the change in the style for a website? (In this case I would deactivate the styles used now).

Dancer18

@Gwen-Dragon It wasn't the panel only. Settings were OK, mods in css and js too.

I decided to update my configuration in Vivaldi stable to the exact same profile (but without this bug!!!) and copy&paste the Default-profile-folder into V snapshot folder.

Now all is fine again and I can enjoy my wonderful browser on next level!

1 remark: I called my son about the issue (he is an excellent programmer) if he knows a brutal fix for it.
He didn't. But we found out that in developer tools writing an inline style with sans-serif fonts was immediately crossed out...