To solve these problems, I highly recommend using Firebug . While you are using firebug, you can debug all kinds of problems. One of the main problems is why my CSS is not connected, or is it so, and I did not code it correctly. You can open firebug. Choose CSS TAB

And look at all the related CSS. You can also look inside the console to find out which error codes are appropriate, they are very detailed and save time.

This will help you deal with these issues. You do not have to use the btw link.
<style type="text/css" src="theme.css"></style>
It works just as well.
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