Writing this issue to keep track of the things we can do / drop once we no longer support IE11. This issue is mainly for record-keeping. Eventually dropping will likely be based on Microsoft ending support for Windows 7, which is currently slated for January 2020.

• Incorporate CSS custom properties into theming
• Drop extra code for sticky positioning and just use position: sticky
• Use IntersectionObserver for overlay positioning
• Use WeakSet instead of WeakMap<T, boolean>
• Second parameter to classList.toggle
• Use element.remove() instead of element.parentNode.removeChild(element)
• Start using CSS Grid, potentially deprecating mat-grid-list
• Start using KeyboardEvent.key / KeyboardEvent.code (re-evaluate cdk/keycodes)
• Explore possibly using native Shadow DOM
• Remove re-implementations of matches and closest
• Get rid of IE-specific cases in InteractivityChecker
• Explore clip-path as a means of custom shapes for components
• Remove IE11-specific fallback animation in mat-spinner
• Can use unset CSS value