Improvements for mobile

[bryanbraun]

Here's what it looks like (very similar between andorid/ios):

Weeks	Years

Possible improvements:

• Add page margin so the graphic doesn't go right up to the edge of the screen on mobile (specifically, the "90" gets cut off, though it isn't shown on the screenshot above).
• Change the day and year fields to use inputmode="numeric" (so the numberic keyboard comes up). See here.