style.css

html, body {
  height: 100%;
}

body {
  display: flex;
  align-items: center;
  justify-content: center;
}

.board {
  width: 375px;
  height: 375px;
}

.board div {
  width: 100px;
  height: 100px;
  min-width: 100px;
  border: 1px #ccc dotted;
  margin: 10px;
  border-radius: 50%;
  background-color: #eee;
  display: inline-block;
}

.board div:hover {
  background-color: #ccc;
}

.totals {
  font-size: 5em;
  font-family: 'sans-serif';
  margin-left: 50px;
}

#blue-total {
  color: deepskyblue;
}

#green-total {
  color: darkseagreen;
}

#invisible-total {
  color: white;
  text-shadow: -1px 0 black, 0 1px black, 1px 0 black, 0 -1px black;
}

div.blue {
  background-color: deepskyblue;
}

div.blue:hover {
  background-color: cornflowerblue;
}

div.green {
  background-color: darkseagreen;
}

div.green:hover {
  background-color: lightgreen;
}

/* Sometimes display: none would be appropriate here. However, because we want the dots
 * to stay in position and take up space, we turn off colour and border instead
 */
div.invisible, div.invisible:hover {
  background-color: white;
  border: none;
}