Css unknown pseudo class for Sololearners

Question

Hello, can you help me where I can learn this pseudo classes?

#cmd:not(:checked) + label + .submenu {
height: 0;
}

What are those? 'not(:checked)'? Never seen here in CSS course, '+' so we can use addition (is any operation can be used?) in CSS?

Udate: I just saw that code here: https://code.sololearn.com/WDnnlWWLf8At/?ref=app

Where I can learn them? Any link?

Answer 1

The 'not(:checked)' refers when a input type checkbox its not checked and the '+ label' means the adyacent label element to the input.
You can search 'css selectors' for more information
https://developer.mozilla.org/en-US/docs/Learn/CSS/Building_blocks/Selectors