Microsoft today announced a new feature in PowerPoint Online. If you are familiar with PowerPoint app on the desktop, you should be aware of the feature which allows you to format slide backgrounds in PowerPoint, which is known as Format Background. Now, Microsoft has delivered this feature in PowerPoint online. Much like in PowerPoint Desktop, you can find the Format Background feature on the Design tab. From there, you can then choose to change your slide background to a solid color or to a picture that is saved on your computer. After you format the background of your slide, you can use the Apply to All option to apply the background of the current slide to all the other slides in your presentation.
Another cool thing about this feature is that it is built by Microsoft interns.The PowerPoint Online implementation of this feature was designed by a program manager intern, coded by a developer intern and has been thoroughly tested by the engineering team to ensure that it meets a high quality bar.
Source: Office blogs