How does a framework like Blueprint CSS keep your site looking consistent from one screen resolution to another?

I've been told to look into开发者_C百科 using a framework like Blueprint or 960 for my CSS.

What I don't understand is how it makes a site look consisent even if two users have different screen resolutions.

How does that work?

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They specify sizes using units that are not relative to the window size. So if the user has a wide window there is a gutter and if a narrow window, a horizontal scrollbar.

Resolution is irrelevant except as a limiting factor on the user's maximum window size.