How to Reduce Header Height?

I have tried to apply this CSS to my website (www.wpspandc.com.au) and although it has reduced the height of the header a bit, it’s still a lot taller than I would like.

I had a look at http://www.zestygift.com/ and the header on this site is about the height I am aiming for (though I don’t know if this is before or after applying the above CSS).

I’ve experimented with everything from a height of 92px down to 5px, but it seems to reach a point beyond which it won’t go any smaller. Why is this?

Is it something to do with the fact that the site tagline is wrapping around and appearing underneath the logo, instead of aligned with the site title?

I want it to be aligned, but don’t know how to achieve this. Any suggestions???

I’ve tried removing my site’s tagline, to see if this was preventing the site-title from reducing in height, but this hasn’t worked. No matter what height I specify for #site-title it doesn’t shrink beyond a certain point.

When specify the CSS code suggested by Alexander, and then reload my site in another tab in my browser, my site briefly flashes up with the shorter header, but then the page instantly refreshes and the header is back to its old height.

It’s almost as if there is another setting somewhere which is overriding the custom CSS setting. Is there somewhere else I should also be making this change to the #site-title attribute?