操作元素属性：element.attribute = new value
element.setAttribute (attribute,value)
element.getAttribute(attribute)
操作样式：elt.style.color = "blue"
elt.style[background-color]/elt.style.backgroundColor
elt.style="color:blue;border:1px solid black"
elt.style.cssText ="color:blue;border:1px solid black"
操作类样式：element.className