The calendar makes table head cells unusable when using Cosmo color theme

[tmortagne]

The calendar seems to force its own style for (all) table head cells, and it does not play well with Cosmo color theme.

To reproduce:

• install calendar pro
• go to admin -> Look & Feel -> Themes -> choose Cosmo color theme -> Save
• go back to the calendar view
• you may need to clear your browser cache

-> you end up with table's head cell with dark grey text on black background (which is obviously not very practical) instead of the expected Cosmo black text on white background
in other pages

[tmortagne]

I cannot reproduce with the 15.9 Charcoal color theme, which is a bit more officially maintained than Cosmo in the dark theme styles.