The part and exportparts HTML attributes expose elements of a shadow DOM as named parts, which can be selected by the ::part() CSS pseudo-element for styling.

The i identifier in a CSS attribute selector matches attribute values case-insensitively in document languages like XML where attribute values are case-sensitive.

The :focus-within CSS pseudo-class matches an element if the element or any of its children are focused.

The :scope CSS pseudo-class matches the scoping root, for instance the element that querySelector() is called on, or the root of a DOM subtree specified with @scope.

The :link CSS pseudo-class matches unvisited links, :visited matches visited links, and :any-link matches both.

The :host CSS pseudo-class selects the containing element of the shadow tree in which it is used. The :host() CSS pseudo-class selects the that element only if it matches the provided selector.

The ::placeholder CSS pseudo-element selects help text in <input> and <textarea> elements when no value is set.

The :placeholder-shown CSS pseudo-element selects <input> and <textarea> elements when no value is set and the element's placeholder attribute is not empty. Not to be confused with ::placeholder, which selects the placeholder text itself.

The :default CSS pseudo-class matches the default element in a group of related form controls, such as checkboxes and radio buttons with the checked attribute.