Themes and Variants in PowerPoint Web Apps
PowerPoint Web Apps is the online (free) version of PowerPoint that has the new Metro interface and features that you will find in the Office 2013 version. One main difference that you may experiment while working with PowerPoint Web Apps is the concept of themes and variants.
Until now, everyone who was familiar with PowerPoint can understand the concepts of templates and themes, but now you can also choose between different theme variants when creating or editing your presentation.
In order to change a theme, you need to pick one from the Design ribbon. Once you choose a theme the variants section will be updated with different color schemes. Applying a variant is a good way to change the presentation style.
If you need PPT templates for the new Office 2013 featuring the default 16:9 resolution, then you can see the changes in free themes PowerPoint 2013.