CSS classes in the grid view

How do I format 2-columns grid cell, consisting of video and its description in order to have:
a) aligned "top" both cells in the row (default is "middle" as in typical table, and it looks bad if descriptions take different number of lines);
b) descriptions of the limited max width, preferably the same as video width?

I had and idea to input "col-1" class in the respective field in grid setting, to make the column slightly wider than a video, but I don't know how to do that (where the CSS class should be written, what syntax, and even if it is a good idea).
Please help.