Firstly, no. Sheet 1 defines P as having 'font-family: sans' and 'font-size: 12pt', then sheet two defines TD as having the same. In your example, only TD gets these attributes.
Secondly, the script's comments tell you (as does the C for Cascading) that any later definition overrides the earlier ones. Something PerlMonk's code takes advantage of. Thus in your example, the script would return 'text-align: center'.