could sb explain why in challenges with CSS graphics (e.g. this one: https://learn.freecodecamp.org/responsive-web-design/applied-visual-design/create-a-graphic-using-css), the top, left, right, bottom properties are all set to zero, and still the div they describe is located in the center of the page? What are they away from at zero distance? And as soon as you delete the properties, the div moves to the top left corner, even though its margin is set to auto, so it should be centered along the horizontal axis, shouldn’t it?
Would appreciate any tips.