Fixed or changeable page size
There are two types of page size formatting in mAuthor:
Fixed — there is one fixed size for all pages in a presentation, which can be set globally in the "Edit CSS" section.
Changeable — each page size can be adjusted individually, depending on the amount of content expected to appear on the page. This option is available in the "Properties" or "Styles" section in the left-side menu where you can manually enter the page size properties.
The option to predefine each page size individually can be found very useful particularly while creating presentations designated for mobile devices. While viewing the content on tablets or smart phones, it is much more convenient and intuitive for users to scroll the page up and down instead of moving on to the next or previous page. In that case, it is highly recommended to predefine each page size individually instead of setting it globally for the whole presentation.