Each Theme contains several unique facets that set it apart from other Themes. These include Theme Fonts, Theme Colors, and Theme Effects. When you apply a different Theme to your PowerPoint presentation, the fonts, colors, and effects applied to your slides change. Unless you override this on a per slide basis, these changes show up in all slides in the presentation. The resulting slides all look consistent. If you explore examples of the same slide with different Themes applied, you will notice that all the slides differ in terms of colors, fonts, and effects applied. Yet the text content is still the same.