The reason may be that this template is using the new and not yet fully supported CSS3. You made the test based on CSS2.1. I made the same test with using the options field and selecting CSS3.
The result, no warnings anymore but still 2 errors. The test on CSS2 showed over 40 warnings that can only relate to CSS3 used!
This is something like a known problem, as no one should by now use CSS3 in a production site as it will always fail the CSS2 validation and CSS2 is the yet current version supported by IE8 and the standard, still.
Check this: http://jigsaw.w3.org/css-validator/validator?uri=http://template15.joomlart.com/ja_mica/&profile=css3&usermedium=all&warning=1&lang=en
About the XHTML validation failout, it is quick done work, not enough time spent to keep the markups correct, the only thing it can be, sorry!