How to create a new slide master in PPT？
1. Click the Design tab > Edit Slide Master > New Slide Master.
2. Click Background in the toolbar to get a pane.
Here we apply Picture or texture fill, set transparency as 43%, and set the font size as 66 for example. You can customize it as needed.
3. Click the Insert tab to insert a picture. In this way we can add duplicate elements in batches.
4. When you have finished, click Preserve Master in the Slide Master tab. In this way, when we delete slides, the master will be saved.