Can the system block past date booking? E.g. user accidentally select yesterday's date.
Yes - login as an admin, go to the Rooms page, select the area you want to change the settings for and then click the Edit icon. Enable min_book_ahead and set the time to zero. To change the default settings for new areas see the comments in areadefaults.inc.php
You seem to have CSS turned off.
Please don't fill out this field.