html {
    background: #018DED url(http://unsplash.it/1500/1000?image=881&blur=50);
    background-size: cover;
    font-size: 10px;
    font-family: 'helvetica neue';
    text-align: center;
}

body {
    display: flex;
    flex: 1;
    align-items: center;
    min-height: 100vh;
    margin: 0;
    font-size: 2rem;
}

.clock {
    width: 30rem;
    height: 30rem;
    margin: 50px auto;
    padding: 2rem;
    border: 20px solid white;
    border-radius: 50%;
    box-shadow: 0 0 0 4px rgba(0, 0, 0, 0.1), inset 0 0 0 3px #EFEFEF, inset 0 0 10px black, 0 0 10px rgba(0, 0, 0, 0.2);
}

.clock-face {
    position: relative;
    width: 100%;
    height: 100%;
}

.hand {
    position: absolute;
    border-radius: 5px;
    transform-origin: bottom;
    transition: all 0.05s;
    /* 可以讓動畫過程擁有 激烈化 或 緩和平順 的視覺感 */
    transition-timing-function: cubic-bezier(0, 2, 1, 1);
}

/**
 * 預設先讓 時針、分針、秒針 都垂直指向 12 點鐘方向
 * 每個寬度與長度都不一樣
 */
.second-hand {
    height: 50%;
    left: calc(50% - 2px);
    width: 4px;
    background: red;
}

.min-hand {
    top: 5%;
    height: 45%;
    left: calc(50% - 3px);
    width: 6px;
    background: black;
}

.hour-hand {
    top: 10%;
    height: 40%;
    left: calc(50% - 5px);
    width: 10px;
    background: black;
}