Learn to use classes

I have made now my first web site with Blocs. Now I like to edit the page for different breakpoints in responsive design. Here the classes come into play. But it don’t work ok or I can’t use the Class manager. I have read the Custom Classes instruction properly.
I have doing the following.
• Open the Class manager. Choosen a font, change the size of the font, choose the color (this time black), choose the line height. Then I choose one text bloc to have the desired text style into it. But the text come “white” . I go back to class editor and check the text color. It seems to be white - but I just have chosen black! I choose the black color again and click done. And still the the text area is whitet! What I’m doing wrong?

Zero answers to my questions! My five days trial period is now end. This time was absolutely to short to find out what kind of Blocs app really can do. Blocs seemed to be interesting but better to wait som time until the software is good enough and most of the bugs have been fixed. I have registered to the mailing list and will come back later.

Did you give the class a proper class name?
And did you put that class name in the text bric?