What is the best method for inserting CSS into a webpage using a Chrome extension?

I am seeking guidance on how to incorporate CSS into a webpage using a Chrome extension. The CSS code I am attempting to inject is as follows:

body {
   background: #000 !important;
}

a {
   color: #777 !important;
}

Here is the content of my manifest.json file:

{
"update_url":"http://clients2.google.com/service/update2/crx",
  "name": "Test Extension",
  "version": "1.0",
  "description": "This extension serves as a test for Google Chrome.",
  "icons": { "16": "icon16.png",
           "48": "icon48.png",
          "128": "icon128.png" },
  "background_page": "background.html",
  "browser_action": {
    "default_icon": "icon19.png"
  },
  "content_scripts": [
    {
      "matches": ["http://test-website.com/*"], 
      "js": ["js/content-script.js"]
    }
  ],

    "permissions": [ "tabs", "http://test-website.com/*" ]

}
javascriptcssgoogle-chromegoogle-chrome-extension

Answer №1

To include additional styling in your Chrome extension, make sure to update your manifest file with the following code:

"content_scripts": [
    {
      "matches": ["http://test-website.com/*"], 
      "js": ["js/content-script.js"],
      "css" : ["yourcss.css"]
    }
],

The specified CSS file under "css": ["..."] will be applied to all pages that match the URLs listed in matches.

If you are working on a Chrome extension, be sure to reference the following resources:

  1. Developer's guide

Answer №2

To easily incorporate a css file into the content of one or more tabs, you can utilize the provided syntax outlined on the Chrome Tabs API webpage:

chrome.tabs.insertCSS(integer tabId, object details, function callback);

First and foremost, you'll need to obtain the ID of the specific tab you intend to target.

Although not explicitly explained in the Chrome Extension documentation, it is important to note that any CSS files injected into a webpage through this method or the manifest file are treated as user stylesheets.

It's worth mentioning that when injecting stylesheets using these techniques, there is a significant limitation (as of Chrome v.19): Chrome does not recognize "!important" declarations within user stylesheets. This means any injected style rules may be overridden by existing page styles.

If you prefer to avoid injecting inline style rules, one workaround involves using the following approach (using jQuery for insertion but adaptable to pure JavaScript):

$(document).ready(function() {
var path = chrome.extension.getURL('styles/myExtensionRulz.css');
$('head').append($('<link>')
    .attr("rel","stylesheet")
    .attr("type","text/css")
    .attr("href", path));
});

Simply store the stylesheet in your extension's styles folder without listing it in the manifest. By leveraging the chrome API to retrieve the stylesheet's URL and setting it as the link's href value, you can elevate the precedence of your stylesheet and utilize the "!important" rule as needed.

For me, this method has proven to be the most effective in the latest version of Chrome.

Answer №3

It appears that chrome.tabs.insertCSS has been deprecated. The recommended approach is to utilize:

https://developer.chrome.com/docs/extensions/reference/scripting/

let [tab] = await chrome.tabs.query({
    active: true,
    currentWindow: true
});

chrome.scripting.insertCSS({
        target: {
            tabId: tab.id
        },
        files: ["button.css"],
    },
    () => {
        chrome.scripting.executeScript({
            target: {
                tabId: tab.id
            },
            function: doSomething,
        });
});

Answer №4

It's actually quite simple. Here is an example:

{
  "update_url": "http://clients2.google.com/service/update2/crx",
  "name": "Sample Extension",
  "version": "1.0",
  "description": "This is just a sample extension for testing purposes.",
  "icons": { "16": "icon16.png", "48": "icon48.png", "128": "icon128.png" },
  "background_page": "background.html",
  "host_permissions": ["*://example-website.com/*"],
  "browser_action": {
    "default_icon": "icon19.png"
  },
  "content_scripts": [
    {
      "matches": ["http://example-website.com/*", "https://example-website.com/*"],
      "js": ["js/content-script.js"],
      "css": ["css/styles.css"]
    }
  ]
}

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