CSS Validation error

Hello,

I am creating a XHTML 1.0 Strict website for class. It validates XHTML and
validated CSS one time. When I revalidated, it kept giving an error and
telling I need to validate my XML document first due to an error on line 54
column 6 h3 has not been closed (</h3>). There is no h3 on line 54 and there
is a properly closed h3 on line 47. What I do not understand is how it
validated CSS at first then does not validate again. no changes were made to
the site. The local file validates, but not the file on the site. Is there
something I am doing wrong? Or is it on your end?

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