This is paragraph of class "a". It's CSS styling rules specify that it should be part of the normal flow, but float w.r.t. the right and maintain a width that is 75% of the window width.

This is paragraph of class "b1". It's CSS styling rules specify that it should remain in a fixed position w.r.t. the top left of the window, although its width can vary.

This is paragraph of class "b2". It's CSS styling rules specify that it should remain in a fixed position w.r.t. the top left of the window, and its width is fixed.

This is paragraph of class "c". It's CSS styling rules specify that it should remain in a fixed position w.r.t. the top left of the window. It's width is fixed. This is a span of class "d". It is positioned relative to the enclosing paragraph "c", but with offsets.

For more information, see this page.