Rated 5 out of 5 stars

It is really easy, untill the developer releases the fixed version, you can do the following:
1) Go to your /extensions/iLeopardMail@reo-2007 or
xp: X:\Documents and Settings\YOURUSER\Application Data\Thunderbird\Profiles\Extensions
vista/win7: %AppData%\Thunderbird\Extensions
or.. wherever is you profile directory containing iLeopardMail@reo-2007 and make a copy of the .xpi file located in iLeopardMail@reo-2007\chrome (e.g. tmp-15.xpi)

2) rename the .xpi file to .zip and extract to [whatever folder]

3) go to [whatever folder]\calendar\widgets and edit minimonth.css, remove max-width: 176px; from the #ltnSidebar { or replace with something like below:

#ltnSidebar {
background: url("chrome://calendar/skin/widgets/Gradient.png") top center repeat-x #dee4eb !important;
width: 190px;
}

4) Repack ONLY the contents of [whatever folder] as a zip file, normal compression, then replace the original .xpi file with your new archive.

Great Theme!
Cheers

This review is for a previous version of the add-on (3.1.2).