Hi,
Regarding the header-like styling. In CSS it works because you create texts with a wide variety of markups h1, h2, p, em, b, span. In LVGL you have only a “label” (like you had only p in HTML).
I also vote to simply add extra styles after creation.
Regarding the odd/even idea: In past weeks I was thinking a lot about supporting something like nth-child selector of CSS. I have some ideas but nothing concrete yet. Finally, it could be used to style individual cells of tables or buttons of a button matrix.