meter {
  /* Reset the default appearance */
  -webkit-appearance: none;
     -moz-appearance: none;
          appearance: none;

  margin: 0 auto 1em;
  width: 100%;
  height: 0.5em;

  /* Applicable only to Firefox */
  background: none;
  background-color: rgba(0, 0, 0, 0.1);
}

meter::-webkit-meter-bar {
  background: none;
  background-color: rgba(0, 0, 0, 0.1);
}

/* Webkit based browsers */
meter[value="1"]::-webkit-meter-optimum-value { background: red; }
meter[value="2"]::-webkit-meter-optimum-value { background: green; }
meter[value="3"]::-webkit-meter-optimum-value { background: green; }
meter[value="4"]::-webkit-meter-optimum-value { background: green; }

/* Gecko based browsers */
meter[value="1"]::-moz-meter-bar { background: red; }
meter[value="2"]::-moz-meter-bar { background: green; }
meter[value="3"]::-moz-meter-bar { background: green; }
meter[value="4"]::-moz-meter-bar { background: green; }