There are a few reasons why your website might be different on GitHub Pages from your local host.

Your Jekyll configuration. GitHub Pages uses Jekyll to generate static websites. The Jekyll configuration file, _config.yml, controls how Jekyll generates your website. If you have different Jekyll configuration files on your local host and GitHub Pages, your websites will be different.
Your assets. Assets, such as CSS and JavaScript files, are not automatically copied from your local host to GitHub Pages. You need to manually add them to the assets directory in your GitHub Pages repository.
Your plugins. If you are using any plugins with Jekyll, you need to make sure that they are compatible with GitHub Pages. Some plugins are not compatible with GitHub Pages, and they can cause your website to look different.
To troubleshoot this issue, you can try the following:

Compare your Jekyll configuration files. Make sure that the _config.yml files on your local host and GitHub Pages are the same.
Check your assets. Make sure that all of your assets are in the assets directory in your GitHub Pages repository.
Disable your plugins. If you are using any plugins with Jekyll, try disabling them to see if that fixes the issue.
If you are still having trouble, you can ask for help on the Jekyll forum: https://talk.jekyllrb.com/.

Here are some additional resources that you might find helpful:

GitHub Pages documentation: https://docs.github.com/en/pages/
Jekyll documentation: https://jekyllrb.com/docs/
Jekyll forum: https://talk.jekyllrb.com/