On Firefox that's "View ... Page Style ... No style." And I do that enough times per day (precious snowflake designers, take note) that I installed the Firefox addon "Disable Style button" which adds a red/white "CSS" stop sign button. https://addons.mozilla.org/en-US/firefox/addon/disable-style...
Honestly, that one button fixes almost every UI/UX problem I encounter. I never use Reader Mode, I never open developer tools, I just nuke styles, read the site and move on.