It really is confidence.
And if you're not lucky enough to have been born in an environment that imbues a natural confidence it can be won but it's harder.
I always thought I was 'naturally confident', and couldn't understand when people weren't, my callous and youthful self thought it was a bit of a personality defect. As I've got older I realise that my confidence comes from a place of privilege in so many ways.
So confidence, it's more a certainty about one's belonging, if you're confident you never feel out of place or as though you shouldn't be there, or listened to, or have your feelings considered.
Looks are secondary really, confident people are at ease with their looks because they're at ease with their place in the world.
And everyone should be confident, we all have equal worth, but as I get older I see how I was given that gift as a child that many people aren't. So work on self-worth and value, ignore the 'nails, hair, brows' crew, sure, if you feel great and worth taking care of, do those things if you feel like it, but preening in itself is not the way to an intrinsic sense of happiness, value and comfort with yourself. And that's the wellspring of confidence.