body {
  margin: 0;
  padding: 0;

  background: #008080;
  color: #222;
  font-family: Arial;
  font-size: 12px;
}

hr {
  margin: 0 auto;
  border: none;
  width: 98%;
  height: 1px;
  opacity: 0.5;
  background: linear-gradient(to right, red 20%, yellow 20%, yellow 36%, green 36%, green 60%, blue 60%, blue 100%);
}

main {
  display: table;
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

.main-window-container {
  display: table-cell;
  vertical-align: middle;
}

.main-window {
  display: flex;
  flex-direction: column;
  
  width: clamp(240px, 480px, 640px);
  height: 100%;
  margin: 0 auto;

  background: #c0c0c0;
}

.main-window-contents {
  margin: 8px;
}

.tab-menu {
  margin: 0 0 8px 0;
}

.tab-contents {
  height: clamp(60px, 120px, 480px);
}

.button-strip {
  display: flex;
  justify-content: flex-end;
}