It has come to my attention that the change in version 10.6 that pushes CSS and JS file loading to the end of the page — which was done to allow the plugin to only load its files when there’s actually a calendar on any given page — may be overwriting some sites’ CSS customizations, depending on where you put those customizations.
I am intending in the next update to add an option to revert to the old way. I would still recommend using the new way as it is more efficient, but I am aware that it can be disruptive if you’ve already established a set of CSS customizations you want to keep as-is.
That said, you may be able to keep your CSS customizations functioning by loading them later (if possible), or by adding
!important to each of the properties.