I used to use http://help.dottoro.com/ when I was learning to program. I would recommend it if someone was looking for a good go-to doc. But for quick reminders (which is rare) I use generally MDN or read the official spec.
They (help.dottoro.com) also have links (when available) to the Microsoft Developer Network, Mozilla Developer Network, Safari Developer Library, and the official W3C spec, which can be helpful. The only thing I would really change about their site is the URL structure. Completely nondescript and not user-friendly.
Once you move from using W3S to MDN or really anything else there is no going back.
They (help.dottoro.com) also have links (when available) to the Microsoft Developer Network, Mozilla Developer Network, Safari Developer Library, and the official W3C spec, which can be helpful. The only thing I would really change about their site is the URL structure. Completely nondescript and not user-friendly.
Once you move from using W3S to MDN or really anything else there is no going back.
CSS's display:
W3S: http://www.w3schools.com/css/css_display_visibility.asp
MDN: https://developer.mozilla.org/en-US/docs/Web/CSS/display
Dottoro: http://help.dottoro.com/lchnsqsb.php