While it is not a hard requirement, it is a practical skill to have and makes you assume the role of ‘Web Designer’. A full stack developer generally has a broad knowledge of a lot of things instead of specializing in one or two things.

You don’t have to be an expert in graphics design either. But knowing the basics can be very useful. Simple things like cropping or resizing an image or adjusting the colors or brightness. But also knowing the difference between the JPG and PNG formats and when to use one or the other. Knowing these basics means you’re less dependent on the graphic designer.

Best of Luck.