Resize image with spacer blocks

I have a tricky issue.  I spent some time with Squarespace live chat to no avail. 

I want to do a standard 'insert spacer block on each side of the image to resize  or centre the image'.

When I insert the spacer blocks and grab one with the mouse, I can clearly see the black insert line horizontally but DO NOT see the black line vertically next to the image.  The image goes almost all the way to the edge.

I have made sure my Chrome browser isnt zoomed in. I have tried using a different browser.

Im using Brine template.   

Beyond grateful if anyone can assist!