defaultTheme 
  fun defaultTheme(typography: StreamTypography = StreamTypography.defaultTypography(), colors: StreamColors = when (isSystemInDarkTheme()) {
                true -> StreamColors.defaultDarkColors()
                else -> StreamColors.defaultColors()
            }): MessageUnreadSeparatorTheme
Builds the default message unread separator theme.
Return
A MessageUnreadSeparatorTheme instance holding the default theming.