What will a regular user see if they insert this layout into a plain HTML document? (an outer div with a red border across the full width, height 100px, inside a square 100x100 with green borders)

The user will see a red horizontal rectangle occupying the full width of the screen and 100 pixels in height. Inside this rectangle, there will be a square of 100x100 pixels with a green border. If the square is not specifically positioned, it will be located in the top-left corner of the outer div, as elements are positioned at the top left by default.

Example of the visual result:

• Outer div: red border, width 100% of the window, height 100px.
• Inner div: 100x100px square with a green border, inside the outer block at the top left.