CSS-only icons in the calendar portlet are used for functionality. Accessibility guidelines indicate that setting icons with CSS (e.g. background, background-image, etc.) is not appropriate for any image that conveys information or provides functionality.
1. Open Firefox to Liferay page containing Calendar portlet
2. Using Web Developer extension: CSS > Disable Styles > Disable All Styles
3. Try to move to the previous/next month or select a drop down menu for a given calendar
Result: Icon or alternative element for function cannot be found
Expected: Icon or alternative element for function is available