adoptStyleSheets method
Applies CSS strings as adopted stylesheets to this component's shadow root.
Uses the modern adoptedStyleSheets API for efficient style management.
On the server, this is a no-op.
Implementation
void adoptStyleSheets(List<String> cssTexts) {
if (_shadowRoot == null) return;
final sheets = cssTexts.map(createStyleSheet).toList();
_shadowRoot!.adoptedStyleSheets = sheets;
}