CSS :target-within

The :target-within pseudo-class was proposed to match an element when it or a descendant is the URL fragment target. It is not broadly supported for production use.

Syntax

section:target-within {
  outline: 0.2rem solid #2563eb;
}

Practical alternatives

section:target {
  outline: 0.2rem solid #2563eb;
}

section:has(:target) {
  outline: 0.2rem solid #2563eb;
}

Result:

Use :target, :has(:target) where supported, or JavaScript for reliable parent highlighting.

Important note

Keep :target-within as a reference item, but avoid presenting it as a normal cross-browser technique.