You can install the web app so it opens from an icon on your home screen or desktop, in its own window. It is the same app you use in the browser, with the same sign-in.
This works on Android, and in Chrome or Edge on a computer.
Open https://polygon.getgps.ru in Chrome or Edge.
An install banner appears at the bottom of the screen.

Select Install, marked 1.
The browser asks you to confirm.
Confirm in the browser's dialog.
The app icon appears on your home screen or desktop, and the banner does not come back.
On iPhone and iPad, Safari does not let a website install itself, so the banner tells you which Safari controls to use.

The close icon on the right of the banner hides it for good in that browser. To install the app afterwards, use your browser's own menu. Most browsers that support installation offer an install or add-to-home-screen option there.
Open the app from its new icon and sign in as usual. Everything works as it does in the browser.