Box Sizing

External references:

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No padding or margin

This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide.
This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide.

With padding, no margin

This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide.
This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide.

No padding, with margin

This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide.
This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide.

With padding and margin

This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide. This is a box that should be 400px wide.
This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide. This is another box that should be 400px wide.