I'd like to add a margin to the top of the window so that it's not so close to the top part of the frame.
How would I go about accomplishing this?
According to the docs, it can't be set individually at the moment. You can play with
internal-border-width which would change all the borders inside the frame. That's what setting it to 7 gives:
(add-to-list 'default-frame-alist '(internal-border-width . 7))
Maybe you'll find a value which would add enough space on top and at the same time small enough that it doesn't affect the sides too much.
tabbar package uses an obscure emacs features called the
header-line to display the tab bar. This
header-line is an extra line of text shown at the top of a buffer, just as the
mode-line is shown at the bottom. The text in this line is rendered using the
tabbar-default face, so you could edit it and change some parameters to customize the look of the tab bar. You could change its font size, or change the font used, for example. Perhaps that will get you close to what you want.
On the other hand, you can't change the line spacing for an individual face, that has to be done for the buffer as a whole. (Curiously, the
line-spacing variable isn't used for the
header-line or the
mode-line, so you can put extra space between all the lines of the buffer except these two.)