* ui: Adds a tab selection animation to our app tabs
1. Replace all mentions of `magenta` with a themeable CSS property.
2. Add an easy way to inline style DOM nodes
3. Use CSS properties to add tab animation
* Fix up rendering test
* Avoid DOM noodling as much as possible
1. Amends our `base` animation placeholder to always reset
transition-duration. This has no effect on other components that are
already using this animation.
2. Adds a confirming class whenever a key is pressed, to show the green
tick. Uses CSS via `transition-delay` for debouncing.