I'm looking for a way for my own Plugin to integrate my own CSS

Good morning

I have programmed my own WordPress plugin. But I don’t like the output in the backend. For example, I want a heading not in black but in white and I want it to be larger.
Since I don’t want to write the styles directly into the code, I need my own CSS file.
The problem is, I don’t know how to integrate a CSS file into my plugin so that it makes my heading bigger in the backend.
Can you give me some tips?

So far I have entered the CSS styles directly into the code.
But I can’t change tables created by WordPress.
For example the style table.widefat

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