Apparently, you cannot use a digit in an ID or CLASS name.
is not ok.
ok then. I just didn’t know and lost 90min figuring it out.
But in the same time I have learned that you can do simple maths directly in CSS, for all your formatting nightmares for responsiveness:
width: calc(33% -[your desired padding for example:] 50px);
Will automatically make the DIVs occupy a third of the page whatever the resolution and have the padding of your choice respected at all times.
Well…. Kinda! Naturally computers don’t understand that if you input 33%, you don’t want the result to sometimes be 33.001%, which will break the layout.
So use 49% for half, 32% for a third, 24% for a quarter… But well, that is a very neat CSS functionality that is largely supported in all modern browser, even Internet Explorer 9 and up.