Sliders on the Campaign theme are type of background. When you want to add a new slider, just create a new section and choose “slider” background for it:
I notice most of the content is responsive but the home page sliders are not mobile-friendly – they keep height so photo doesn’t show everything. Is there any CSS code to fix this?
Reason is simple: Campaign sliders are not sliders, but section backgrounds as explained previously, so it is planned to be below other objects – sign up or contact forms, i.e.
If you want to have regular sliders, you can always use a third-party plugin. Master slider has a free version which allows to create responsive slider with images and thumbnails. If you want to have more advanced effects and object animations, you will need to use one of premium plugins.