You can customize the theme of your BotStacks UI kit by modifying the defaults of the BotStacksThemeEngine. The theme supports fonts, colors, assets, and dimensions. Configure it like this:

BotStacksThemeEngine(
    // true or false to force theming one way (default follows system)
    useDarkTheme = isSystemInDarkTheme(),
    // color scheme for light mode
    lightColorScheme = lightBotStacksColors(
        primary = Purple40,
        onPrimary = Color.White,
    ),
    // color scheme for dark mode
    darkColorScheme = darkBotStacksColors(
        primary = Purple80,
        onPrimary = Color.Black
    ),
    // fonts to utilize for Text within components
    fonts = with(Typography.bodyLarge) {
        botstacksFonts(
            body1 = FontStyle(
                size = fontSize,
            )
        )
    },
    // assets for empty state and logo (in header)
    assets = Assets(
        logo = R.drawable.inappchat_icon,
        emptyChat = EmptyScreenConfig.Messages(
            caption = "No messages yet."
        )
    ),
    // shape definitions for components
    shapes = ShapeDefinitions(
        small = 4.dp,
        medium = 10.dp,
        large = 16.dp
    )
) {
    // content code here (components, Controller)
}