nostr:npub1j46f9va5qdrmamcwmncew7g8mwekgma386dhws6k04fsnlkqpcpsj23gm7 The Sass documentation makes this clearer because it shows examples (and Sass invented this syntax).

div {
  .foo {
  }
}

Becomes `div .foo` (note the space between).

div {
  &.foo {
  }
}

Becomes `div.foo` (no space between).

https://sass-lang.com/documentation/style-rules/parent-selector/