DM section has a different background color in dark theme in active narrow

[shubham-padia]

While addressing comment, I noticed that direct messages section has a different background color in the following condition:

• Dark mode
• Actively narrowed into the section.

Other sections in the sidebar (e.g. topic list filter) use the --color-background-active-narrow-filter css variable. DM section also uses the same value as the variable in light mode (without explicitly using the variable)

CZO thread