是这样的：闲着没事写了一个把洛谷上所有用户名颜色全改成紫色的油猴脚本，结果有些改掉了，有些没改掉，这是怎么回事？代码如下：

// ==UserScript==
// @name         test
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  try to take over the world!
// @author       Rain wang
// @include      https://www.luogu.com.cn/*
// @grant        none
// ==/UserScript==

(function() {
    'use strict';
    var a = document.getElementsByClassName("lg-fg-brown");
    var b = document.getElementsByClassName("lg-fg-gray");
    var c = document.getElementsByClassName("lg-fg-bluelight");
    var d = document.getElementsByClassName("lg-fg-green");
    var e = document.getElementsByClassName("lg-fg-orange lg-bold");
    var f = document.getElementsByClassName("lg-fg-red  lg-bold");

    for (var i = 0; i < a.length; i++)
    {if (a[i].target) a[i].className = "lg-fg-purple lg-bold";};

   for (var j = 0; j < b.length; j++)
    {if (b[j].target) b[j].className = "lg-fg-purple lg-bold";}

    for (var k = 0; k < c.length; k++)
    {if (c[k].target) c[k].className = "lg-fg-purple lg-bold";}

    for (var p = 0; p < d.length; p++)
    {if (d[p].target) d[p].className = "lg-fg-purple lg-bold";}

    for (var q = 0; q < e.length; q++)
    {if (e[q].target) e[q].className = "lg-fg-purple lg-bold";}

    for (var o = 0; o < f.length; o++)
    {if (f[o].target) f[o].className = "lg-fg-purple lg-bold";}

})();