Because h1 tags are block level elements you can specify a height for them. In this case you didn't and the default height is a little taller than you would like. To solve this just add these style rules to your other h1 style rules:
line-height: 18px;
height: 18px;
The text should immediately drop down, then all you have to do is fiddle around with the padding until you get it how you want it.