How do you edit multiple classes of bootsrap?

I have started with boostrap and created a new css file after bootsrap.min.css and I’m adding in new css file the new style i want to change , but have been able to edit only the container of navbar becauser navbar wasn’t possible to edit as there are many classes with different navbars and have tried to tag .navbar but didn’t worked and I have no idea how to tag the current navbar on my page.

Below is HTML and CSS with boostrap own CSS content

What are trying to change? If you are just changing a few things on navbar it should not be too hard to do.