Adding to this: without any specification, the browser should, and does, use the operating system's native controls when rendering controls such as <button>.
https://blog.chromium.org/2020/03/updates-to-form-controls-a...
All part of Google's master plan to commoditize desktop OSs. Everyone outside the US already uses Android, soon your computer will be a Chrome box instead of a Windows/Mac/Linux box.
First they did the browser title bar & tab bar integration/styling & removed the normal OS title bar, then they made Chrome OS, now they are removing the last traces of OS-specific styling for those who haven't already switched to Chrome OS.
And Gmail, Gdocs, and Chromebooks are huge in kids schools. The kids don't know anything outside the non-Google universe. Most of the kids I know think MS Word/Excel/PowerPoint are lame (not that I'm a fan, but you have to admit MS Office is unrivaled in its abilities).
20 years from now they will have a gigantic monopoly over a huge range of computing.
I'm hoping Firefox Foundation or something like that will do some work in this area.
And I think that web applications should be like this. They may be delivered differently, but they should be part of the system like everything else. Making the UI elements look like the OS ones is good.
I especially notice it on KDE, since on the default KDE theme the checkboxes and radiobuttons and scrollbars look a bit different from most other OSs and the Gnome default theme. But in the browser my checkboxes and radiobuttons and dropdowns look exactly like every other checkbox and radiobutton and dropdown on my computer, and the scrollbars have the distinctive KDE look too.
Most web apps do behave differently from normal applications, and also have stupid company-specific theming, but it's nice having at least parts of them fit in.
I suspect those who come from a Windows background will not have the same opinion, because on Windows basically every app is a mess of different themes and window decorations.
Now that CSS and Javascript are so widely used, it would be interesting for OS vendors to provide a default OS theme along with their packaged browser, that allowed some kind of sane default for web applications to use. You could use a native skin, or load your own CSS to customise it. Microsoft kind of tried this with ActiveX controls, and then Java Applets tried it, and then Flash was fun by ultimately not a good idea, and now we're here with thousands of themes to choose from and a rough set of guidelines that some follow and many don't.
I'm not worried. Mozilla/Microsoft used to be in a similar position with Firefox/IE at one time.
Now they're both playing second fiddle to Chrome. The only constant in tech is that everything changes.
Wait until they reach the age and get hired in a corporation. I am a die hard linux user ( been on linux desktop more than i can remember ), but the latest stuff (=365) from MS is really appealing compared with gSuite. It has a level of sophistication that Google cannot reach.
My experience disagrees, as long as we're not talking about Electron or UWP applications. Your description sounds exaggerated.
Right now I'm running Outlook, Firefox, Solidworks Electrical, Solidworks, Skype for Business, and ECi M1. Outlook uses the latest style ribbon and flat UI, Firefox uses its own style for everything, Solidworks Electrical uses the old style ribbon UI with panes and stuff from I think .NET toolkits, Solidworks uses its own ribbon and UI theme that's unique to it, Skype is inexplicably blue with its own blue icons, M1 uses its own ribbon style and has somewhat standard controls on a gray background, with a custom tree view that scrolls horizontally when you click on things...
I also have PLC and HMI programming software. Omron CX-Programmer, Sysmac Studio, and NB-Designer, which all look different from each other and any of the other software I'm running.
I think it's harder for me to pick two programs that look alike than it is to find ones that look different.