Dark theme: Fix composer border color
Dark theme: Fix composer border color

Signed-off-by: Jan-Christoph Borchardt <7f550a9f4c44173a37664d938f1355f0f92a47a7@jancborchardt.net>

ChristophWurst/mail,ChristophWurst/mail,kingjan1999/mail,kingjan1999/mail,ChristophWurst/mail,kingjan1999/mail