Personally, not a fan of this style of theme. It looks too boxy and generic, perhaps even a bit dated. I think it could use a bit more white space in certain areas. Grid pages, like this one, feel especially claustrophobic.
I do like the attention to detail. Things like the breadcrumbs, author box, “you might also like” section (how are those being pulled in, by the way?), selection color, hover/focus effects, and other little details, all make it evident you put a lot of work into this theme.
Best of luck with it.
I’ve seen this before. I actually like it when done right, as it makes the visible area less constrained when the user doesn’t “need” it, which is especially helpful on mobile when every last pixel counts.
That’s not quite what’s happening here though. Sometimes I see the header appear when scrolling down too. Seems odd to me.