How to change new topic's layout on mobile side?


I am would like to consult how to change layout of new topic’s composer on mobile side.
As almost of my potential user has no PC and only mobile phone, so improve UX on composing from mobile device is quite a key point to me.

Actually there is only one thing I want to do is increase the blue area.

Here is my idea:
Remove below area and replace to input-title. I guess in almost of discourse community there only this option right?


Any one could tell me which file should I modify?

I read this one already and it’s more like for adding new eletment/change element’s size.
Hope if there are any guide for modify layout.
Beginner’s guide to developing Discourse Themes - documentation / theme developers - Discourse Meta