First thing, try jsbin -- here's your html and css in a jsbin:
JS Bin - Collaborative JavaScript Debugging[
^]
Here's the code:
HTML
<h1 id="centerMe">My First Blog!</h1>
CSS
#centerMe{
text-align:center;
}
and if you wanted all your H1 tags to be centered you could do:
h1{text-align:center}
Check it out at the JSBIN -- change it to whatever you want and you'll see it live.