Minor fixes & mobile landscape styling

Hi all! I made a couple minor fixes to the UI:

• more precise centering on the 'Next' button
• indenting on the UL for mobile (portrait)

I also added styling for a mobile landscape mode. This new section can be found at the very bottom of the Stylesheet under 'mobile landscape' and includes: 

• tweaks to the dialog boxes to display correctly with the shorter screen height
• a scrollbar for the dialog boxes
• adjustments to the footer menu and notifications

Have fun!!