checkbox & radio button style with visibly larger hit area

[benguhin]

Starting this out as a separate issue from #236

I've been pushing this specifically for mobile devices (see #232 ), but it's also so much nicer on desktop to have big, spaced options to select from when the primary task is choosing between options in a list.

Here's a screenshot of a not-very-styled prototype we built for our complaint forms, which tested really well:

Gov.uk has their style for this documented here: http://govuk-elements.herokuapp.com/#form-radio-buttons

If we go forward with this as an optional variation for checkboxes and radio buttons, there are a few things to define:

• Default state on a white background
• Default state in a fieldset (gray background)
• Hover state
• Selected state
• Placement and rules for helper copy within each option
• Rules for width, stacking, and columns across breakpoints

I think @ajbush has already given this some thought

[caheberer]

This is standard practice for us now. Closing this issue, we're adding this update to the manual as part of the form fields exploration in #346.