Post Header Formatting Problem

[conrad1on]

Hello. I'm having trouble changing the colour, size etc. of the date
header for my posts in my blog.

Changing values in 'Fonts and Colours' doesn't do anything, and
neither does altering the template directly. In fact, I removed this
chunk of code from the template altogether:

.Blog h2.date-header {
margin-top:10px;
margin-$endSide:0px;
margin-bottom:0px;
margin-$startSide:0px;
color: $dateHeaderColor;
font-size:120%;
text-align: $startSide;
text-transform:none;
font-weight: bold;
}

... and nothing changed - the posts still had a date heading, but the
formatting still matched the text in the actual post. This seems to be
relevant actually, as changing the size of the text used within posts
also changes the size of the date header.

I'm not sure what I may have broken here, but I was forced to move
that chunk of code manually, as the date header was originally
appearing underneath the post titles. However I've since moved the
code back where it was, but obviously it's had no effect.

Any suggestions would be appreciated, but I should point out that I'm
not hugely familiar with HTML and the like.