You can add a border, such as a picture frame or a dotted line, around an image, shape, text box, or video, then modify the border’s thickness, color, and other attributes.
Select an image, shape, text box, or video.
In the Format 
sidebar, click the Style tab.
Click the disclosure triangle next to Border, then click the pop-up menu and choose a type of border (line or picture frame).
Use the controls that appear to adjust the look of the border.
To add a border—such as a solid or dotted line—around a page, you first add a square shape to the page, then change the shape’s attributes so it behaves like a border. For example, you 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 page, and so on.
Click 
in the toolbar, then select the square or rounded rectangle from the Basic category.
Drag the white squares that appear around the shape until the outer edges of the shape form the border size you want.
In the Format sidebar, click the Style tab.
To remove the color from the shape or choose a different color, click the pop-up menu below Fill, then click No Fill or choose a different fill option.
Click the disclosure triangle next to Border, then click the pop-up menu and choose a type of border (line or picture frame).
To change the transparency, 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.