[misc] Updated page to the new XAR format
XWIKI-10932: Try to have the same height for "Variables" and "Preview" boxes on Flamingo Theme

* Increasing the height mannualy
XWIKI-10932: Try to have the same height for "Variables" and "Preview" boxes on Flamingo Theme

* Added a ‘row’ container in order to hold the grid elements, thus
better aligning components
* Removed ‘div’ from the id selectors