A modal over everything in HTML & CSS
HTML & CSS interview exercise on Positioning & stacking, difficulty 2 of 3. Solve it in the editor beside a worked example, or cold in Interview mode with the example hidden; the tests run the moment you do.
The overlay must cover the whole viewport with a translucent dark layer, stay put while the page scrolls, and sit above the sticky header. Centre the dialog inside it, both ways, at 360px wide.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Interview mode hides the example: solve it from memory, without the hint or the solution, and it counts as solved cold. Progress is saved in your browser, and in your account if you sign in.