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Key Concepts [Jan. 23, 2012, 11:52 p.m.]


Margin Collapsing

Top and bottom margins of blocks are sometimes combined (collapsed) into a single margin whose size is the largest of the margins combined into it, a behavior known as margin collapsing.

For example:

#section1 { margin: 1.5em 0 1.5em; } /* top, right/left, bottom */

#section2 { margin: 2.5em 0 1.5em; } /* top, right/left, bottom */

The winnning margin where the two sections separate is 2.5em because it is the largest value.