Hi Arthur & manicolaus,
If I understand your problem correctly, you could try this:
Go to ‘Appearance’ > ‘Editor’ > select ‘Stylesheet’ (right hand column, bottom) then append this at the end of the stylesheet…
#content, #content input, #content textarea { width: 460px; }
.pushbutton-wide { width: auto; }
I tried it out and it seemed to work ok.
– C.