Reworked the CSS.
Availability date is not required when the product is available.
Prevent XSS attacks by filtering the content before inserting to DB.
Use open_form_multipart where appropriate, instead of open_form and set
the type.
Remove "method" => "post" as it is redundant. open_form already does it.
Do not create the element if it already exists. It might already exist
if the user clicked once on the button but not all the required fields
were filled in.
Do not submit the form. This will be done by the submit button.
Use from_* for improved security.