Code Changes: Adding your own styles
CSS (style changes) can be made in the 'design' tab of the app, or in your theme's CSS. Or if you are looking to create your own bundle template you can use Template Creator - only advisable if you are an experienced developer with liquid coding skills.
Here's where you would head to find the "design tab":
3. Bundle Builder
6. Scroll down to "Custom CSS"
You can edit your theme's code by heading here:
2. Online Store > Themes
3. Actions > Edit code
Here is a great Shopify help document if you need it:
A benefit of using the app's built-in "Custom CSS" area is that if you decide to change your theme, the code will remain in the app itself, rather than be erased by the new theme install.
You can find the Template Creator here:
1. Admin > Apps > Bundle Builder
3. Template Creator