code: function resetMirror({mirror, source, options, ...args}) {
    return withPromise((resolve) => {
      let offsetHeight;
      let offsetWidth;
  
      if (options.constrainDimensions) {
        const computedSourceStyles = getComputedStyle(source);
        offsetHeight = computedSourceStyles.getPropertyValue('height');
        offsetWidth = computedSourceStyles.getPropertyValue('width');
      }
  
      mirror.style.position = 'fixed';
      mirror.style.pointerEvents = 'none';
      mirror.style.top = 0;
      mirror.style.left = 0;
      mirror.style.margin = 0;
  
      if (options.constrainDimensions) {
        mirror.style.height = offsetHeight;
        mirror.style.width = offsetWidth;
      }
  
      resolve({mirror, source, options, ...args});
    });
  }
docs: Applys mirror styles
  @param {Object} state
  @param {HTMLElement} state.mirror
  @param {HTMLElement} state.source
  @param {Object} state.options
  @return {Promise}
  @private