Every presentation has a theme; some are just more colorful than others.
The theme determines the look and colors of your slides and gives your presentation a consistent appearance. Here, you see three title slides that have the same content but that use different themes.
A theme includes these elements, offered as a package:
- Background design
- Color scheme
- Font types and sizes, and
- Placeholder positions
The color scheme affects background colors, font colors, fill colors for shapes, border colors, hyperlinks, and slide elements like tables and charts.
Regarding placeholders, the theme honors the layout you've chosen, it just moves things around a little. For instance, on the three slides shown, each theme puts the title and subtitle placeholders in a different position. But the basic Title Slide layout is still there.