A few online HTML page viewers. Last two are a discussion of how to read page code, and Dave's Site.
https://www.computerhope.com/issues/ch000746.htm How to read HTML
https://www.davesite.com/webstation/html/ My long time favorite HTML tutorial / practice page, Dave's Site. You may be blinking rapidly the first minute or two, with all the ads, fonts, and colors, but get used to that and see all the offerings..