calendar: add css class 'inactive' to mark inactive entries

scripts/md2ical.py

@@ -26,7 +26,7 @@ def extract_lecture_dates(markdown_file, output_file):
     for table_entry in soup.findAll("tr")[1:]:
         date, title, lecturers = [e.contents[0] for e in table_entry.findAll("td")]
 
-        if lecturers == "-":
+        if lecturers == "-" or table_entry.find(class_="inactive"):
             # Table entries without lecturer are considered to be breaks/holidays.
             continue
 

styles.css

 /* css styles */
+
+tr:has(.inactive) {
+    opacity: .5;
+}