function updateDefaultHighlight() {
		$w.find("button, input").removeClass("default");
		let $default = $(document.activeElement).closest("button, input[type='submit'], input[type='button'], textarea, select");
		if ($default.length === 0) {
			// Buttons in forms default to type="submit" implicitly.
			$default = $w.$form.find('button[type="submit"], input[type="submit"], button:not([type])').first();
		}
		if ($default.is("button, input[type='submit'], input[type='button']")) {
			$default.addClass("default");
		}
	}
@param {string | Node} label
@param {()=> void} action
@param {object} [options]
@param {string} [options.type]
@returns {JQuery<HTMLButtonElement>}