如何注入CSS以隐藏谷歌浏览器中的某些div块？

Question

我正在尝试删除div元素“pagecountBlock”，一旦我在网站上查看5个页面，它就会隐藏内容。我在线跟踪了几个线程无济于事，我想知道如何在网站上注入和应用css。谁能告诉我这里我做错了什么？感谢。

的manifest.json

{
    "name": "CollegeProwler Ad Hide",
    "description": "Hides Ads on CollegeProwler",
    "version": "1.0",
    "manifest_version": 2,
    "icons": {
        "24": "logo24.png",
        "128": "logo128.png"
    },
    "content_scripts": [ {
        "matches": ["http://collegeprowler.com/"], //where script should be injected
        "css": ["hideAd.css"], //the name of the file to be injected
        "js": ["hideAd.js"] //js script to inject css
    } ],
    "web_accessible_resources": ["hideAd.css"]
}

hideAd.css

div .pagecountBlock {
    display: none !important;
}

div .lockCount {
    display: none !important;
}

hideAd.js取自this thread

var style = document.createElement('link');
style.rel = 'stylesheet';
style.type = 'text/css';
style.href = chrome.extension.getURL('hideAd.css');
(document.head||document.documentElement).appendChild(style);