gristlabs_grist-core/app/client/ui/App.css

html {
  height: 100%;
  overflow: hidden;
}

body {
  height: 100%;
  font-family: sans-serif;
  font-size: 1.2rem;
  margin: 0;
  padding: 0;
  background: var(--grist-theme-bg, url('img/gplaypattern.png'));
  background-color: var(--grist-theme-bg-color, unset);
}

.g-help {
  position: absolute;
  top: 10%;
  left: 10%;
  height: 80%;
  width: 80%;
  z-index: 999;

  padding: 1rem;

  background-color: rgba(0, 0, 0, .8);

  -webkit-border-radius: 1rem;
     -moz-border-radius: 1rem;
          border-radius: 1rem;

  color: #fff;
  font-size: 1.4rem;
  overflow: auto;
}

.g-help-table {
  width: 100%;
  margin-bottom: 2rem;
}