How to place 3 columns beside each other on mobile

Hi.
I’d like to show coloumns beside each other on mobile, etc
– instead of under each other.
How do I do that?

I’ve given each column a css class: targetmenu
And written this in the code:

I doesn't work, though....
Tried to give the row the class: targetmenu instead.
- but that didn't work eighter.

Can't seem to get the system..
Can you help?

- Maiken