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: yellow; }
meter[value="3"]::-webkit-meter-optimum-value { background: orange; }
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: yellow; }
meter[value="3"]::-moz-meter-bar { background: orange; }
meter[value="4"]::-moz-meter-bar { background: green; }