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