body{
    margin: 0;
    height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    background: linear-gradient(#666, #333);
}

.loader {
    width: 8em;
    height: 10em;
    font-size: 20px;
}

.train {
    width: 6em;
    height: 6em;
    background: 
        radial-gradient(circle at 20% 80%, currentColor 0.6em, transparent 0.6em),
        radial-gradient(circle at 80% 80%, currentColor 0.6em, transparent 0.6em),
        #bbb;
    border-radius: 1em;
    position: relative;
    left: 1em;
    color: #444;
    animation: train-animate 1.5s infinite ease-in-out;
}

@keyframes train-animate {
    0%, 100% {
        transform: rotate(0deg);
    }

    25%, 75% {
        transform: rotate(0.5deg);
    }

    50% {
        transform: rotate(-0.5deg);
    }
}

.train::before {
    content: '';
    position: absolute;
    width: 80%;
    height: 2.3em;
    background-color: currentColor;
    border-radius: 0.4em;
    top: 1.2em;
    left: 10%;
}

.train::after {
    content: '';
    position: absolute;
    width: 25%;
    height: 0.4em;
    background-color: currentColor;
    border-radius: 0.3em;
    top: 0.4em;
    left: calc((100% - 25%) / 2);
}

.track {
    width: 8em;
    position: relative;
    color: #bbb;
}

.track::before,
.track::after {
    content: '';
    position: absolute;
    width: 0.3em;
    height: 4em;
    background-color: currentColor;
    border-radius: 0.4em;
    transform-origin: bottom;
}

.track::before {
    left: 0;
    transform: skewX(-27deg);
}

.track::after {
    right: 0;
    transform: skewX(27deg);
}

.track span {
    width: inherit;
    height: 0.3em;
    background-color: currentColor;
    position: absolute;
    top: 4em;
    animation: track-animate 1s linear infinite;
}

.track span:nth-child(2) {
    animation-delay: -0.33s;
}

.track span:nth-child(3) {
    animation-delay: -0.66s;
}

@keyframes track-animate {
    0% {
        transform: translateY(-0.5em) scaleX(0.9);
        filter: opacity(0);
    }

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

    100% {
        transform: translateY(-4em) scaleX(0.5);
        filter: opacity(0);
    }
}