* Optimize mx_RoomView_myReadMarker
- Replace the compound selector with a type selector
- Nest the type selector in "mx_RoomView_myReadMarker_container"
* Conform the style rules to the naming policy
Including "container" in a class name is redundant as our naming policy tells that a string followed by an underscore (_) represents a container if it contains an element.
* Run prettier
* Replace `mx_RoomView_myReadMarker hr` with `mx_RoomView_myReadMarker`
- Remove a unit
- Hide hr's parent (mx_RoomView_myReadMarker) on Percy snapshots
* Change the class name from `mx_RoomView_myReadMarker` to `mx_MessagePanel_myReadMarker`
The read marker is specified on MessagePanel.tsx, and should be named so to avoid confusion.
- Create _MessagePanel.pcss for the style rules of MessagePanel
* Update permalinks.spec.ts
