You should try this plugin: https://elfsight.com/instagram-feed-instashow/#preview (link to the demo). It gives you lots of layout settings, and full control over the color of each element. You might not even need to add your own styles!
But if you still want to, you can always customize any element using your own styles. You just need to make necessary changes to your main styles file, they will be used for the plugin as well.
You can check the installation guide here https://elfsight.com/help/how-to-add-instagram-feed-plugin-for-webflow/.
I hope it was helpful! If you have any further questions, feel free to ask!)