Minor style/visual tweaks

Reduce the opacity of the placeholder text in the message text area so emojis in channel names don't stick out. This would also mean making the placeholder text color brighter in dark mode so normal characters don't contrast less with the background.

The icon for "unable to load profile profile banner, badges, and about me" seems too visible. Maybe make it gray?

Basically posted by others, but I may as well include it:
A bunch of symbol emojis (trademark, end, mathematical signs, eye in speech bubble, et cetera) have far too little contrast with the dark mode background. This one is more major.

These suggestions apply to the web version, at least. Not positive about the desktop one.