Why custom.css file does not work?

Hello,

I want to modify a style in base.css file (line 250):

#top #wrap_all .error .text_input, #top #wrap_all .error .text_area, #top #wrap_all .error .select {
     border: 2px solid # ff0000;
}

This would be the change I want to make. I enter the code in custom.css and does not modify it. But if I enter the new code in quick css if accepted.

The funny thing is that if I modify the same code in your source file (base.css) nor the modification is performed.

Why does this happen?

Greetings.