text: class Button {
    constructor(element){
      this.element = element;
      this.element.addEventListener('mousedown', () => this.mouseDown());
      this.element.addEventListener('mouseup', () => this.mouseUp())
    }
    mouseDown(){
      this.element.classList.remove('shadow-animated');
    }
    
    mouseUp() {
      this.element.classList.add('shadow-animated');
    }
  }
  
  let buttons = Array.from(document.querySelectorAll('.btn'));
  buttons.map(button => new Button(button));