This div is floated left

The width for this div is set to 70%. Red borders are here to help you visualize its size and position

This div appears first in the document source.

Normally, when an element is floated left, the following elements wrap around it. Wrapping is prevented here because sidebar div occupies the space left empty by the width: 70% rule.

Sidebar div

This div, outlined in blue, has a width of 25% assigned to it. The other rule needed to create the columnar effect is a margin-left: 75%. The width and margin-left rules combine to create a column that will not wrap around the floated div element.

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