Upstream requires at least two additional sources. Whereas Invidious needs it to be
able to display a single additional source for normal (dashless)
qualites. Aka medium and hd720.
This will prevent, on large pages, the LTR and RTL text to be
far away, on each side of the page. This could happen on channel
and playlists descriptions, when the page is displayed on a large
screen.
Adding these styles is the easiest way to add bidi (bidirectional text) support without or with least side effect. I have tested it by adding it manually on yewtu.be instance and so far it works very well.
Now that themes are controlled with a class instead of setting
media="none" on the stylesheet link and both themes already being
duplicated in default.css for the automatic themeing it makes sense
to have all theme related CSS in the same place.
This commit also fixes the missing dark theme on embeds.
Themes are now controlled with a class on the body element.
If a preference is set the body element will have either "dark-theme"
or "light-theme" class. If no preference is set or the preference is
empty the class will be "no-theme".
"dark-theme" and "light-theme" are handled by darktheme.css and
lighttheme.css respectively.
"no-theme" is handled by default.css where depending on the value of
"prefers-color-scheme" the styles corresponding to "dark-theme" or
"light-theme" are applied.
Unfortunately this means that both themes are duplicated, once in the
theme .css and once in default.css.
syeopite