This is a DNN issue when using canonical portal aliases in multiple (dev/testing/staging/production) environments.

On my staging server, I loaded an exact copy of a production site using localhost. When SmithCart was upgraded locally, I noticed all the buttons were tiny and grey and changing the themes did not work. Looking at the source HTML, I realized that DNN was referring to the production server instead of localhost as intended.

Workaround

Select Admin|Site Settings|Advanced|Portal Aliases and adjust the canonical portal alias to localhost (or your configured portal alias).

SmithCart works as expected under these specific conditions.