Add New Offcanvas Functionality

Allow Offcanvas to overlap content instead of pushing content.
Code Reduction
Add New Offcanvas Functionality 

Allow Offcanvas to overlap content instead of pushing content.
Add Vendor Prefixes for CSS transform

Add Vendor Prefixes for CSS transform.

Many thanks to @diggy for finding there was a problem in my Pen on Chrome.

Silly me for forgetting to put the vendor prefixes.
Merge pull request #5035 from winghouchan/new-offcanvas-functionality

New offcanvas functionality