Модальное окно
Пример №1
See the Pen Modal window only JavaScript - EasyToggler.js #1 by Emil Rakhmatullin (@rah_emil) on CodePen.
Выпадающее меню
Пример №2
See the Pen Dropdown menu only JavaScript - EasyToggler.js #2 by Emil Rakhmatullin (@rah_emil) on CodePen.