How do I tuck my corporate motto under my site name in CSS?

No, the CSS positioning that you have in your style is going to mess things up, coupled with the spacing that the h4 and p tags force on your layout too. I would skip the h1 and p and I and use CSS instead. Like this:

Now, in your CSS you can do something like this:

See what I'm doing? Let the CSS do all the spacing and line height work and you'll find that you have complete control over your spacing. Further, recall that margin AND padding control the space around the contents of a container like "div", so you need to tweak it below the top one AND above the bottom one.

Try that, see if it helps you get where you want. Note, however, that if you make your URL clickable then you have a more complicated issue with formatting because you can't just use the formatting in the ID, but need to touch the style itself. Quite doable, but more tricky...