multilingual blog

Dear supporters,

I am in the process of building a website. I migrated parts of my old Squarespace website to WordPress without problems. However, when I reached the blog, I ran into trouble. I imported all the posts onto my static page. Some posts are in English, others in Swedish. Given that I can only have one static site, all the posts are mixed, but of course, I would like to have them separated. Therefore, I assigned them into categories, which I can link to, so one page only displays the English posts, whereas another page only displays the Swedish posts. The problem, however, is the following: whilst my static site is nicely formatted with the theme layout (zakra), the pages displaying the categories seem to have no layout at all. And I have been unable to find an option to change the layout of the categories. Will have have to adapt the CSS code or is there another option? If I have to, how do I do this best?
I would greatly appreciate some help. Thank you in advance and best wishes.