To filter your global CSS file for styles used in a specific HTML file in VS Code:

• Use a CSS Purge Tool : Install and configure a tool like PurgeCSS or UnCSS to analyze your HTML and remove unused CSS.
• Manual Filtering : Open the HTML file, inspect elements in the browser's developer tools, and manually copy relevant CSS selectors and properties from your global CSS.
• Extensions : Use VS Code extensions like CSS Peek to help identify and manage styles.

For the most efficient method, use a CSS purge tool.