Some code tricks...

This (main content) area is "span-17". But it's also class="colborder" which adds a vertical rule on the right that takes up another column. That leaves 6 columns for the right sidebar. The last column in a row (which by default has 24 columns), needs the class @.last@ to remove its left hand margin. Note, however, that each @.span-24@ don't need the @.last@ class, since these always span the entire width of the page.

Horizontal rules? "lessthan" hr / "greaterthan"

The adjacency combinator (a plus sign, +) allows you to style an element if it has been directly preceded by another specified element. I ended up not using this, but "p + p" defines a style for all paragraphs except the first (all paragraphs that follow a paragraph).

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Four images, each four columns wide, and a gray bar for the 17th column.