💄(react) make Modal close button sticky

We want to make sure this button is always visible inside scrollable
modals.

Fixes #278

packages/react/src/components/Modal/index.tsx

@@ -132,7 +132,7 @@ export const ModalInner = (props: ModalProps) => {
                 <Button
                   icon={<span className="material-icons">close</span>}
                   color="tertiary-text"
-                  size="nano"
+                  size="small"
                   onClick={() => props.onClose()}
                 />
               </div>