How to hang a style on an element only if it has a certain class?

Hello. Stood in a stupor.
There is a div that has some classes.
How to do in css so that the style only worked if there is certain classes?
For example as it happens with children by type
.parent .child { ...}
Or with the next .nbr1 + .npr2

PS
Thanks to all, turns out it was the spacebar
April 4th 20 at 13:18
2 answers
April 4th 20 at 13:20
Solution
.class0.class1 {}
April 4th 20 at 13:22
Solution
.class_one.class_two {
 # no space between the classes
}

Find more questions by tags CSS