You have Separate layout for each and everything this makes your work easy
check out this
Hope it helps!
There is a option to change the width for layout.
about front-end part, this course can help you: https://gettingstarted.mendixcloud.com/link/path/105/Style-your-App-with-CSS .
And about back-end part, you can find more help in this learning path: https://gettingstarted.mendixcloud.com/link/path/56/Create-an-App-with-Advanced-Page-Building