Material design support that views are drawn on top of other views by assigning an elevation level to them. Your styles.xml would also be the right place to add more themes-which in turn you could preview in Android Studio. The Android platform provides a new theme, new widgets and new API for custom shadows and animations. These colors get used by the theme generated at project creation, looking like this in styles.xml: could also remove the reference and edit the colors in the theme directly, but that is usually not the clean way. Locate your colors.xml in res/values/ and modify the colors there: Here you can see the background and color scheme for all three themes. Choose the right theme from the drop-down and click on Apply and then Ok. Under the Appearance & Behaviour -> Appearance, you will find Theme. A new Settings dialog will appear, like this. Usually this would be the AppTheme that is referencing some colors. To change default themes go to File and click on Settings. To actually change the colors you need to change the theme.

It does not change the theming on your phone when running your app-it is just a preview.

This is used to view how your layout would look using a given theme. You are changing the theme of the preview window.

Android studio theme change