Using themes, you can apply the same layout, appearance and formatting to data models when you need all models with the same look. Theme provides you with a color scheme but you can customize it as per the requirement.
To apply a theme, go to Format → Theme
From the theme list, select the theme and you can see the preview of that theme in the preview window. Your model is updated as per the theme properties.
You can also set that theme as the default theme for your model. To set a theme as default, go to File → Preference
Go to Document → Under Components → Select Theme from drop down list → OK.