:not selector in CSS [duplicate]

Answer 1

That's because :not(.c1) will select any element that doesn't have that class. That can be the .container too.

Either add a direct child combinator:

:not(.c1) > .text {
  font-weight: bold;
}

Or use the other class as well:

.column:not(.c1) .text {
  font-weight: bold;
}