I'm hoping to get some help with what should be an easy question: how do I inherit a core theme?

After looking at the docs it seemed that by creating a .info file and setting the base theme I would have inheritance set up. I tried that with this:

name = development - testing theme based on Garland
core = 6.x
base theme = garland

After activating this theme I lost all styles. The base theme directive seems to do nothing. My theme is in sites/all/themes/garland-dev; garland is in themes/garland. Please advise.

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La perfection est atteinte non quand il ne reste rien à ajouter, mais quand il ne reste rien à enlever.
— Antoine de Saint-Exupéry