Yes, Microsoft offers Sticky Notes on Windows 10 and 11, and judging by the number of comments, it's one of the most popular apps in its store. However, if you're looking for an independent alternative that works exclusively in your browser and lets you add virtual sticky notes on specific sites, you might want to try WebStickies, available for Chrome/Chromium and Firefox.

WebStickies: Virtual Sticky Notes for Your Favorite Websites
WebStickies

The quickest way we have to 'take a note' on a web page is simply to save it as a favorite. Of course, with that we run the risk of the classic 'favorget' – that is, burying the link among other favorites and forgetting it completely. A good alternative comes from the real world: digital Post-It notes, virtual versions of the typical sticky notes. And with that idea in mind, we discovered WebStickies, an extension compatible with Google Chrome and Mozilla Firefox.

WebStickies: Virtual Notes on All Your Pages

WebStickies: Virtual Sticky Notes for Your Favorite Websites
These notes are excellent for summarizing articles and highlighting their most important aspects

Once the extension is installed, its main keyboard shortcuts are three: Alt + Shift + N to create a new note, Alt + Shift + O to open the quick settings menu, and Alt + Shift + L takes you to that same menu in a separate tab. The sticky notes essentially behave like mini windows or dialog boxes that float on a web page. If you right-click on the top bar of a note, that will open its secondary options, among which the font size, the reset for its size and position, minimize/maximize, and the colors (six in total) stand out.

WebStickies: Virtual Sticky Notes for Your Favorite Websites
WebStickies supports six different colors, which also work as categories to separate content
WebStickies: Virtual Sticky Notes for Your Favorite Websites
You can edit the properties of each note at any time

All WebStickies notes are saved locally and persist, so they'll still be there if you close the tab or the browser (unless you're particularly dedicated to resetting their condition with each new session). At the same time, the extension supports limited cloud sync, with a maximum of 64 notes for its free edition. Personally, I think local mode is much more robust, but if your browsers are already linked, you should take a look.

WebStickies: Virtual Sticky Notes for Your Favorite Websites
All notes will be grouped together here

WebStickies is a relatively new extension, and there are still features in the pipeline (such as dark mode), but I think it deserves your attention, even at this early stage of development. Download a copy!

Official site: Click here