.sf-btn {
&_size_s{
width: 100px;
}
&_square{
border-radius: 0;
}
&_square&_size_s{
width: 110px;
}
}
sf-btn_square
→ sf-btn_type_square
The negation pseudo-class, :not(X), is a functional notation taking a simple selector (excluding the negation pseudo-class itself) as an argument