前端每日實戰：104# 視頻演示如何用純 CSS 創做一個貨車 loader

效果預覽

按下右側的「點擊預覽」按鈕能夠在當前頁面預覽，點擊連接能夠全屏預覽。

https://codepen.io/comehope/pen/vaPGRz

可交互視頻

此視頻是能夠交互的，你能夠隨時暫停視頻，編輯視頻中的代碼。

請用 chrome, safari, edge 打開觀看。

https://scrimba.com/p/pEgDAM/cz32DUd

源代碼下載

每日前端實戰系列的所有源代碼請從 github 下載：

https://github.com/comehope/front-end-daily-challenges

代碼解讀

定義 dom，容器表明卡車，包含的 2 個子元素表明車頭和尾氣；<hr> 表明道路：

<div class="truck">
    <span class="cab"></span>
    <span class="smoke"></span>
</div>
<hr>

居中顯示，同時道路與頁面之間留出空間：

body {
    margin: 10%;
    padding-top: 10%;
}

畫出卡車車箱：

.truck {
    width: 15em;
    height: 5em;
    font-size: 10px;
    background-color: #444;
    border-radius: 0.4em;
}

用僞元素畫出車箱的車輪：

.truck {
    position: relative;
}

.truck::before,
.truck::after {
    content: '';
    position: absolute;
    box-sizing: border-box;
    width: 2em;
    height: 2em;
    background-color: #444;
    border: 0.1em solid white;
    border-radius: 50%;
    bottom: -1em;
}

.truck::before {
    left: 0.6em;
}

.truck::after {
    right: 0.6em;
}

畫出車頭：

.cab {
    position: absolute;
    width: 3.3em;
    height: 2.5em;
    background-color: #333;
    left: -3.5em;
    bottom: 0;
    border-radius: 40% 0 0.4em 0.4em;
}

.cab::before {
    content: '';
    position: absolute;
    width: 2em;
    height: 1.5em;
    background-color: #333;
    top: -1.5em;
    right: 0;
    border-radius: 100% 0 0 0;
}

畫出車頭的車輪：

.cab::after {
    content: '';
    position: absolute;
    box-sizing: border-box;
    width: 2em;
    height: 2em;
    background-color: #444;
    border: 0.1em solid white;
    border-radius: 50%;
    bottom: -1em;
    left: 0.5em;
}

畫出尾氣的初始狀態：

.smoke,
.smoke::before,
.smoke::after {
    content: '';
    position: absolute;
    width: 1em;
    height: 1em;
    background-color: #333;
    right: -0.1em;
    bottom: -0.5em;
    border-radius: 50%;
}

增長排出尾氣的動畫：

.smoke {
    animation: smoke-1 2s infinite;
}

.smoke::before {
    animation: smoke-2 2s infinite;
}

.smoke::after {
    animation: smoke-3 2s infinite;
}

@keyframes smoke-1 {
    to {
        width: 3em;
        height: 3em;
        right: -3em;
        bottom: 0.5em;
    }
}

@keyframes smoke-2 {
    to {
        width: 2.5em;
        height: 2.5em;
        right: -6em;
        bottom: 0.8em;
    }
}

@keyframes smoke-3 {
    to {
        width: 3.5em;
        height: 3.5em;
        right: -4em;
        bottom: 0.2em;
    }
}

增長尾氣的飄散效果：

.smoke {
    animation:
        drift 2s infinite,
        smoke-1 2s infinite;
}

.smoke::before {
    animation: 
        drift 3s infinite,
        smoke-2 3s infinite;
}

.smoke::after {
    animation: 
        drift 4s infinite,
        smoke-3 4s infinite;
}

@keyframes drift {
    0%, 100% {
        filter: opacity(0);
    }

    15% {
        filter: opacity(0.9);
    }
}

增長卡車行駛的動畫效果：

.truck {
    animation: 
        move 5s infinite;
}

@keyframes move {
    0% {
        margin-left: 90%;
    }

    50% {
        margin-left: 45%;
    }

    100% {
        margin-left: 0;
    }

    0%, 100% {
        filter: opacity(0);
    }

    10%, 90% {
        filter: opacity(1);
    }
}

增長卡片行駛中顛簸的動畫效果：

.truck {
    animation: 
        put-put 2s infinite,
        move 10s infinite;
}

@keyframes put-put {
    0% {
        margin-top: 0;
        height: 5em;
    }

    5% {
        margin-top: -0.2em;
        height: 5.2em;
    }

    20% {
        margin-top: -0.1em;
        height: 5em;
    }

    35% {
        margin-top: 0.1em;
        height: 4.9em;
    }

    40% {
        margin-top: -0.1em;
        height: 5.1em;
    }

    60% {
        margin-top: 0.1em;
        height: 4.9em;
    }

    75% {
        margin-top: 0;
        height: 5em;
    }

    80% {
        margin-top: -0.4em;
        height: 5.2em;
    }

    100% {
        margin-top: 0.1em;
        height: 4.9em;
    }
}

大功告成！