Often, your work is not done! A code reviewer can request changes in your code. If you tested your code before making a pr, this is often to correct style or to avoid known caveats.
Remember: if your pull request receives a "needs changes" review, this means your code is useful and good -- otherwise somebody would have closed your pr without a second look.*
Work with your code reviewer, and integrate the requested changes. Once you are ready, you can re-request your reviewers review.
Especially when first contributing to a repo, you may have to complete this cycle a couple times. Just remember that it gets easier as you become more familiar with the standards of a code-base! :)
* addendum: this does not mean your code is bad if your code is rejected. Hopefully, code rejections come with good, friendly explanations from responsible maintainers. If your code is rejected for bad reasons, remember you can always contribute to another project :)
There is no such thing as one, correct style guide (except for in go).
There is such thing as one, correct style guide for a codebase.
Be ready to adopt certain code styles with which you disagree.
It is incredibly valuable to have a code-base that follows the same style rules -- no matter how silly they may be.
Of course, feel free to voice your opinions to try and change the style guide. Just realize that extreme style overhauls will be rejected in a heartbeat. You must be willing to adopt code styles while you are working on an open-source project.