use CSS to position element element of widget
@memberof DOMWidget
function place() {
    var containerWidth = this.container.getWidth(),
        containerHeight = this.container.getHeight(),
        width = this.width <= 1 ? containerWidth * this.width : this.width,
        height = this.height <= 1 ? containerHeight * this.height : this.height,
        x = this.x < 1 ? containerWidth * this.x : this.x,
        y = this.y < 1 ? containerHeight * this.y : this.y;

    if (!this.attached) {
      this.attached = true;
    }

    if (this.isSquare) {
      if (height > width) {
        height = width;
      } else {
        width = height;
      }
    }

    this.element.width = width;
    this.element.style.width = width + 'px';
    this.element.height = height;
    this.element.style.height = height + 'px';
    this.element.style.left = x;
    this.element.style.top = y;

    /**
     * Bounding box, in absolute coordinates, of the DOMWidget
     * @memberof DOMWidget
     * @instance
     * @type {Object}
     */
    this.rect = this.element.getBoundingClientRect();
  }