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.