How to move the Full Editor screen around?

To move the full editor drag it in the middle (vertically) of the top border (for example, try to click and drag on the ‘hypatia’ title).

Other options :
Choose the right size of the full editor in the Options (available in the mini editor). There are 3 choices: small, medium, and large.

If the math you want to type is small, you can also use the mini editor in the sidebar directly.