CSS Code:

#overlay .map .name{
  display: inline; /* This is what turns ON the title */
  background-color: rgba(0, 0, 0, 0.7); /* This allows you to change the background color and transparency, where 0,0,0 is black and 0.7 is the transparency */
  color: #fff; /* This is the font color, where #fff is white */
  font-size: 12px; /* This is the font size in the title */
}

Preview: