var span = document.getElementById("today");

//  设置内容

　span.innerText = "天空好像下雨";
    span.innerHTML = "<font color='deepskyblue'>天空好像下雨</font>";

//设置属性

　span.setAttribute("color","green");

//设置样式

　 span.setAttribute("style","font-family: 幼圆;");