Heading size of paragraph

In This Example the header is not the normal si开发者_JAVA技巧ze of a header. Please explain.

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See the "Normalized CSS" checkbox on the left? It's using a CSS reset.

From the jsFiddle docs:

[...]Next is the Normalized CSS checkbox, selected by default. If selected, the fiddle will be rendered with normalize.css which is removing most of the browser styling of many HTML tags.