html, body {
    margin: 0;
    padding: 0;
    background: #3F51B5;

    font-size: 1em;
    font-family: Helvetica, Arial, sans-serif;
}

.mast-head {
    font-size: 1.5em;
    text-align: center;
    margin: 20px;
    color: #fff;
}

a {
    display: block;
    padding: 10px;
    color: #eee;
}

button {
    padding: 10px;
    font-size: 1.5em;
    margin: 20px;
    background: yellow;
}
button[disabled] {
    background: gray;
}

/* hides the button when in standalone mode 
    (opened from HS icon - however, this must 
    mean that HS icon always opens in standalone mode,
     ie.e manifest display mode is actually set to that)
     */
@media all and (display-mode: standalone) {
  #a2hsBtn {
    display: none;
  }
}