Kzmus.site is a browser-based tactic designed to trick users into subscribing to push notifications from a rogue website. When people visit this page, they see a black screen and some unknown content loading; however, to view that content, Kzmus.site asks visitors to click on the 'Allow' button and agree to receive notifications. This is a common technique to get permission to deliver advertising messages to users' computers or phones directly.
Pop-ups generated by Kzmus.site are very likely to contain links to potentially harmful websites. They typically promote suspicious online products and services, like gambling and porn websites, fake software or Potentially Unwanted Applications (PUAs).
To delete Kzmus.site's permission to send you advertisements, open the Settings menu of your browser, go to the section that concerns your online privacy, then find and remove the website. If the annoying advertisements keep showing up, you may need to check your device for adware or other PUAs. These can run intrusive advertising campaigns. Many of them also have data-tracking features and also can cause severe privacy issues.