lib/index.esm.js
function getStyle(el, key) {
  return (el.currentStyle || document.defaultView.getComputedStyle(el, null))[key] || el.style[key];
}
function getStyle(el, key) {
  return (el.currentStyle || document.defaultView.getComputedStyle(el, null))[key] || el.style[key];
}
读取HTML元素样式值
@param {HTMLElement} el 目标元素
@param {String} key 样式key
@return {String}