To add a border around a slide, you first add a square shape to the slide, then change the shape’s attributes so it behaves like a border. For example, you can change the size of the shape, give it no fill (as opposed to a color fill) so that it doesn’t obscure other objects on the slide, and so on.
Click 
in the toolbar, then choose the square or rounded square.
Drag the selection handles until the outer edges of the shape form the border size you want.
Click the Style tab at the top of the sidebar on the right.
If you don’t see a sidebar, or the sidebar doesn’t have a Style tab, click 
in the toolbar.
To remove the color from the shape or specify a different color, click the pop-up menu next to Fill, then click No Fill or choose a different fill option.
To specify what the border looks like, click the disclosure triangle next to Border, then click the pop-up menu and do one of the following:
Choose Line, then choose a line style from the pop-up menu below it. Click the color well to change the color of the line, and click the arrows to change the thickness of the line.
Choose Picture Frame, then choose a picture frame style from the pop-up menu below it. Use the Scale slider to adjust the thickness of the frame.
To change the transparency of the border, drag the opacity slider.
To lock the border so it doesn’t get moved accidentally, click the Arrange tab at the top of the sidebar, then click Lock.
