Styling Imported Blog Posts in Custom Theme

I am having a lot of trouble figuring out how to style custom blog posts I’ve imported (along with images) into the “blog” portion of a website recently migrated onto wordpress using a custom theme.

The theme contains a very basic blog page template copied below. The issue is that all of the posts I try to import become very basic and unappealing (compare blog.lisalindblad.com with “lisalindblad.theatomgroup.com/blog/”). Is my only option really to try and learn how to code the php template from scratch so it mimics the current site and then style it? From there, how would I go about mimicking functionality?

Really the only purpose of this transfer is to migrate the content of the blog on to the new website. I can’t fathom that there isn’t an easier way to do it, but all of my searching has come up nil. Any help would be VERY much appreciated!