<snip>
And when you restart caching, I'd remove manually all files in the /sites/default/files/css/ directory.
</snip>

I deleted all those files, some 86 of them, then made a couple of changes in the /sites/all/modules/calendar/css/calendar.css and calendar_multiday.css  then hit refresh in the browser and the
/sites/default/files/css/ was rebuilt but with different names and no change to the calendar display and interestingly did not include my changes to the aforementioned files but defaults back to the original.

/sites/all/modules/calendar/calendar.info shows
files[] = calendar.install
files[] = calendar.module
files[] = includes/calendar.views.inc
files[] = includes/calendar_plugin_style.inc
files[] = includes/calendar_plugin_row_node.inc
files[] = theme/theme.inc
files[] = theme/calendar-style.tpl.php
files[] = theme/calendar-row-node.tpl.php

I checked out theme/calendar-row-node.tpl.php but to me it is no help.

I'm thinking the calendar module seems not well considered in that it writes once to the css file and will not include manual changes - I have not a clue how to fix the issue.

I did notice that if, in firebug, I make the display field very wide, 25em and about 5em high it contains all of the views fields and that changing any of those to the top of the views fields list, it sometimes displays those changes but there is no way to make the change permanent.

Trouble is the little blue default display in calendar is far too small to contain useful information, font is bold and hard to read.
Roger