body {
  margin: 0;
  padding: 0;
  background: rgba(0, 0, 0, 0.669);
  font-family: Arial, Helvetica, sans-serif;
  color: white;
  overflow: hidden;
}

#controls {
  position: absolute;
  top: 10px;
  left: 10px;
  border-radius: 8px;
  background: rgba(0, 0, 0, 0.538);
  padding: 12px 16px;
  font-size: 14px;
  line-height: 1.4;
}

#controls h2 {
  margin: 0 0 6px 0;
  font-size: 16px;
  color: #ffffff;
}

kbd {
  background: #3f3f3f;
  padding: 2px 6px;
  font-size: 12px;
  border-radius: 4px;
  font-family: monospace;
  color: #ffffff;
}

#toggleTheme,
#toggleMassNumbers,
.speedBtn {
  margin-top: 10px;
  padding: 6px 10px;
  cursor: pointer;
  border-radius: 8px;
  background: #3f3f3f;
  color: white;
  font-weight: bold;
  border: none;
}

#toggleTheme:hover,
#toggleMassNumbers:hover,
.speedBtn:hover {
  background: #2d2d2d;
}

#massControl {
  margin-top: 10px;
  font-size: 13px;
}

#massSlider {
  width: 120px;
  vertical-align: middle;
}

#massValue {
  display: inline-block;
  min-width: 20px;
  margin-left: 6px;
  font-weight: bold;
}

#speedControls {
  margin-top: 12px;
}