Zoom content not screen with Magic Mouse
Sorry,i never saw Content before(too rush),,CMD + Magic mouse scroll in most cases doesn't increase the font size, 'zoom' in. Increasing the font size system wide isn't possible without setting it specifically for Applications (if you know the menu title) in keyboard shortcuts. However, you can emulate a system wide zoom in level with a double tap of the mouse (using magic mouse) by turning that system feature on in:

System Preferences > Mouse > Smart Zoom

But still Incase of screen,,Go to System Preferences > Accessibility, and in the list on the left click the item "Zoom".

Then make sure that feature is enabled (checkmarked) in the pane on the right, and that Control has been set as the modifier.

Then Just hold down the [control] key, then slide your finger to the top or bottom of the mouse, and you’ll zoom in and out just like you would with a mouse scroll wheel.

Hope this solves your problem!