As explained in the Important section of the documentation, there are two sets of require() that are needed before you require the calendar itself.
The first [$CSS=1;], which has to be called inside of the <head> tag, is there to apply the theme styles to the calendar. You can customize your theme by editing the esstyle.css that's found in /calendar/theme/*your_theme*/
The second one [$OL=1;], which can be called at any point between the <body> tag and the actual calendar, is there to include the code required for the overLib (mouse-over) popups to work.
If there's any other info you'd like, don't hesitate to ask.
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