That is the correct behavior for CSS Sculptor 3. If you define any styles for your spry components in Sculptor, it will overwrite the default Spry styles. The page loads the default Spry CSS first, then anything you define in Sculptor. If we did it the other way, your changes in Sculptor might never show up.
To fix your specific issue, it sounds like you can just move the Spry CSS include after the Sculptor CSS include in your page. Then it will load the Sculptor CSS first, then the Spry CSS.