body {
  height: 100vh;
  background: green;
}

body.loading, body.loading * {
  cursor: progress !important;
}

h1 {
  color: white;
}

a {
  cursor: pointer;
  color: white;
}

window.setLoadingFlag = function () {
  window.isLoading = true;
  document.body.className += ' loading';
};

window.removeLoadingFlag = function () {
  window.isLoading = false
  document.body.className -= ' loading';
};

var bodyStyle = document.body.style

setInterval(() => {
  if (window.isLoading) {
    bodyStyle.background = 'green';
    removeLoadingFlag();
  } else {
    bodyStyle.background = 'blue';
    setLoadingFlag();
  }
}, 1000)