'how to prevent shortcut key event alt + '=' in browser

i am developing contenteditable editor in web browser

i want to prevent alt+'=' shortcut key event in browser(like chrome, edge, firefox)

When I press the alt+'=' key, the css effect disappears and the letter spacing becomes wider as in the image below.

It even appears in the browser address bar as above.

The onKeydown event is not controlled, and the Keydown event itself does not occur.

how to prevent alt+'=' shotrcut key event

javascript browser

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