Hi Carly, Thanks for contacting us. This can be achieved using the Pro tab > Pro Editor tool > Pixlr Editor:
– On the left toolbar select the Drawing tool (yellow rectangle and circle icon around 1/2 way down the toolbar in the 2nd column)
– Untick “Fill Shape” on the top toolbar and select the “Border Size”
– You can also change the color down the bottom of the left toolbar (by clicking the black rectangle below the hand icon)
– Lastly, draw on the rectangle, and when you’re done click the File menu > Save and then the OK button
Let us know if you have any further questions!