After customizing colors, fonts, effects, or backgrounds, you can save your design as a custom theme. This allows you to reuse the same professional look in future presentations.
Methods to save a Custom Theme
Method 1: Save the Current Theme (Easiest Way)
Step 1: Open the presentation that has the customized design you want to save.
Step 2: Go to the Design tab.

Step 3: In the Themes group, click the More arrow (the small drop-down arrow) to open the full Themes gallery.

Step 4: At the bottom of the gallery, click Save Current Theme.

Step 5: In the Save Current Theme dialog box:
- Type a clear name for your theme.
- Keep the file type as Office Theme (*.thmx).

Step 6: Click Save.
Your custom theme will now appear under the Custom section in the Themes gallery.
Method 2: Save Theme from Slide Master View
Step 1: Go to the View tab and select Slide Master.

Step 2: On the Slide Master tab, click Themes.

Step 3: Select Save Current Theme.

Step 4: Enter a name and click Save.
How to Use Your Custom Theme Later
Step 1: Open any presentation (new or existing).

Step 2: Go to the Design tab and select Themes.
Step 3: Scroll to the Custom section.

Step 4: Click your saved theme to apply it.

You can also right-click the custom theme and choose Set as Default Theme so every new presentation starts with your design.