Why Am I Unable to Inject CSS into Webpages Using Content Scripts for Extensions?

CSS Injection Issues in Content Scripts for Extensions

Despite defining CSS injection in the manifest, your CSS file remains absent from the webpage. Here are the possible causes and solutions:

Reason: Conflicting CSS Rules

The style sheet is injected but not applied due to other styles overriding its rules.

Solution:

• Increase CSS Specificity: Add more specific selectors to your CSS rules.
• Use "!important": Suffix every rule with "!important" to override existing styles.

Reason: Content Script Injection Limit

Manifest version 3 limits content scripts from directly injecting CSS.

Solution: Inject CSS via a content script as follows:

myScript.js:

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

manifest.json:

"web_accessible_resources": ["myStyles.css"]

Note: When using Manifest version 2, the "web_accessible_resources" key is required to allow access to the CSS file from a non-extension page.

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