Css styles donot work well inside headers

Question

I have placed some content inside the header tags.If i apply css styles to the content inside the tags means,the header comes down.what can i do for this?
CSS styles:
header
min-height: 120px;
background: #9EA5CF;
#maintitle {
    color: #FFF;
    padding-left: 50px;
    padding-top: -20px;
HTML Code:
<header>
  <h1 id="maintitle">LORUM IPSUM</h1>
</header>

Answer 1

Murray, on the second part of your post (default margins), I think that is the case when I use images as the target for a live link (in IE) ... I have to go in and set the 'border' to 0.
Actually, a simple rule for this in all browsers is -
a img { border:none; }
That will prevent any image that is also a link from having a border. And it's definitely not just in IE.
On the first part, all I know is when I first started doing some naming of IDs and Classes, my computer told me not to go there, so I don't.
Now, that could easily be because I had no clue what was really going on.
I prefer to think of it as your just being new to CSS, but yes - that's most likely it. Can you give us a specific example?
HTML4 or HTML5 should not affect how you USE your CSS.