Pattern Lab UIKit Bug Fixes

[sghoweri]

Summary

Misc bug fixes + cross-browser related updates to Pattern Lab's UI

Before

Note the extra whitespace on the left and right sides when viewing on a notched device like the iPhone XS Max

Safari UI bug with the dropdown buttons + global UI bug with the background color

IE 11 rendering bug with the side nav layout

After

Full screen support + responsive UI layout via the new viewport-fit meta tag + CSS env constants: https://css-tricks.com/the-notch-and-css/

Fixed dropdowns + fixed default <button> styles in Safari

Fixed layout bugs in IE 11

Details

In particular, this PR:

1. Fixes several mobile, Safari and IE 11-specific issues encountered in local dev testing (like default browser-specific styles for buttons and input elements)
2. Fixes major scrolling issues seen on mobile devices while still fixing the IE 11-specific issues that unintentionally caused the bugs in the first place
3. Implements iframe resizer functionality to Pattern Lab to bring much more native-like scroll functionality + much better performing scrolling as a result
4. Better mobile support for devices with curved / notched screens (iPhone X, iPhone XS and iPhone XS Max)
5. Fixes a UI bug relating to missing background colors in the nested Pattern lab navigation

Testing Instructions

Compare Pattern Lab's UI that's currently live with the updates from this branch -- especially on Safari and on mobile devices!

[bolt-bot]

⚡ PR built on Travis and deployed a now preview here:

• Branch link: https://feature-pl-uikit-fixes.boltdesignsystem.com
• Permalink: https://boltdesignsystem-gwthqotjqy.now.sh

• Commit built: 37ab4ca
• Travis build

[bolt-bot]

⚡ PR built on Travis and deployed a now preview here:

• Branch link: https://feature-pl-uikit-fixes.boltdesignsystem.com
• Permalink: https://boltdesignsystem-obsdfumfev.now.sh

• Commit built: 2cd3f3a
• Travis build

[bolt-bot]

⚡ PR built on Travis and deployed a now preview here:

• Branch link: https://feature-pl-uikit-fixes.boltdesignsystem.com
• Permalink: https://boltdesignsystem-nhosxzshun.now.sh

• Commit built: bc6151f
• Travis build