exporting css into a .html file

[Greg Minshall]

hi.  i'm wondering what the reference to "style blocks" means in the
"CSS Support" section of the manual:
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For longer style definitions, either use several ‘HTML_HEAD’ and
‘HTML_HEAD_EXTRA’ keywords, or use ‘<style> ... </style>’ blocks around
them.  Both of these approaches can avoid referring to an external file.
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can anyone provide enlightenment?  thanks!