Style editor match closer to aegisub's

Currently, the style editor menu is very long, and is also missing a preview. It might be a good idea to closer match how aegisub does it, as screens are going to be wider than taller in general.

<img width="402" height="680" alt="Image" src="https://github.com/user-attachments/assets/291e128b-65cc-4f94-a01e-63f04b6a99ec" />