html sizing

For these pages I am displaying html flipbooks with short code.

Will the theme allow me to change vertical sizing? I tried to use css in WordPress and it wouldn’t work. I am not so skilled in that arena.

Reference:

https://azlegion.org/historic-department-of-arizona-documents

https://azlegion.org/historic-department-of-arizona-documents-2

The page I need help with: [log in to see the link]