@keyframes blinker {
    50% {
      opacity: 0.3;
    }
  }

.timer {
    font-size: 8em;
    font-weight: bold;
    text-align: center;
    line-height: 1.2;
}

.timer.over {
    color: #0f0;
    animation: blinker 2s ease infinite;
} 

main {
    height: 100vh;
}

main > div {
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
}