Why isn't my CSS working? Understanding specificity and the override mechanism

I added CSS, but the text color and margins didn't change.It worked when I rewrote the same specification at the bottom of ...
Ars Technica

CSS: 'display:none;' isn't it supposed to hide form elements from being submitted?

I'm working on a web app with some dynamic forms, that show certain fields based on different form selection choices and different button combinations. Up until now, I had been designing those ...