Theme lives on Settings → Preferences. Choose Light, Dark, or System. The page says "Applies to this browser on this device."
Pick Light, Dark, or System
Theme is your browser on this device. Teammates keep their own preference. It does not change workspace name, seats, or tokens.
Open Settings → Preferences.
Find the Theme heading.
Select Light, Dark, or System.
If System is selected, the hint is "Currently dark on this device." or "Currently light on this device."
There is no notifications settings how-to. Settings → Notifications redirects to General.
Theme does not change LinkedIn, Unibox, or Account Protection. It does not apply to the marketing site for other people. It does not change seats, tokens, or who can finish a LinkedIn check.