Firstly, all that CSS should be in a separate file which is included by adding one line into the page header:
Code:
<link rel="stylesheet" type="text/css" href="your_style_sheet.css">
Secondly, there are better solutions than copy and pasting the same code into 50 different files. The old fashioned way was to use Server Side Includes and either rename your source files to .shtml or use XBitHack if your server is Unix (see here). However, a much simple solution is to simply rename your .html files as .php and then use the PHP include directive to add the requisite file at the correct place in your source file.
Code:
<?php include 'myfile.html'; ?>
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