Sidebox heading settings should be standardised in your stylesheet.css under .leftBoxHeading and/or .rightBoxHeading, whether or not prefaced with a heading tag, eg h3.leftBoxHeading.

You may have to specify a font-size and other font display properties under your .leftBoxHeading and/or .rightBoxHeading in stylesheet.css, as I have in mine.

However, in my setup, I notice the calendar sidebox heading is defined as <h3 id="eventscalendarHeading" class="rightBoxHeading">, but since I have no #eventscalendarHeading defined in any of my *.css files, this part really does nothing.

Hope this helps.