Editing h1, h2, h3

When rewriting the wiki.css, h1, h2, and h3 are not changing when I write new declarations.

I have tried simply writing

h1 { font-size: 1em; }

Then I stepped it up to

#displaycontent h1{ font-size: 1em; }

and neither of those worked. However, when I used the second code I wrote in the tester CSS program supplied by PBwiki, it worked perfectly.
 
indifferent I’m perplexed
Inappropriate?
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