So I missed this deal too, but just got an email with this code, bringing the Responsive HTML course cost to $15.
Terms and Conditions
* Coupon not valid with any other promotional offer or discount
* Coupon may be used multiple times until the expiration date
* Only one coupon per purchase
* Coupon is not exchangable for cash
* Coupon not valid with purchases made on the Udemy iPhone or iPad app
Courses Excluded from the discount can be found here