DevExpress WPF themes only affect on gauge appearance when a gauge uses a themeable model. For this, assign a CircularThemeableModel object to the CircularGaugeControl.Model property to apply the theme to the Circular gauge. To apply themes to the Linear gauge, assign a LinearThemeableModel object to the LinearGaugeControl.Model property. Then, you can use ThemeManager to set a specific theme to all the elements in the application's window or a separate control. For this, specify the required theme's name using the ThemeManager.ThemeName option.
The following markup shows how to apply the DXStyle theme to the entire window: