.sky {
    height: 50vh;
    position: relative;
    overflow: hidden;
    top: 60%;
}
.clouds_one {
    background: url("images/cloud_one.png");
    position: absolute;
    left: 0;
    top: 0;
    height: 100%;
    width: 300%;
    -webkit-animation: cloud_one 100s linear infinite;
    -moz-animation: cloud_one 100s linear infinite;
    -o-animation: cloud_one 100s linear infinite;
    -webkit-transform: translate3d(0, 0, 0);
    -moz-transform: translate3d(0, 0, 0);
    -o-transform: translate3d(0, 0, 0)
}

.clouds_two {
    background: url("images/cloud_two.png");
    position: absolute;
    left: 0;
    top: 0;
    height: 100%;
    width: 300%;
    -webkit-animation: cloud_two 150s linear infinite;
    -moz-animation: cloud_two 150s linear infinite;
    -o-animation: cloud_two 150s linear infinite;
    -webkit-transform: translate3d(0, 0, 0);
    -moz-transform: translate3d(0, 0, 0);
    -o-transform: translate3d(0, 0, 0)
}

.clouds_three {
    background: url("images/cloud_three.png");
    position: absolute;
    left: 0;
    top: 0;
    height: 100%;
    width: 300%;
    -webkit-animation: cloud_three 175s linear infinite;
    -moz-animation: cloud_three 175s linear infinite;
    -o-animation: cloud_three 175s linear infinite;
    -webkit-transform: translate3d(0, 0, 0);
    -moz-transform: translate3d(0, 0, 0);
    -o-transform: translate3d(0, 0, 0)
}

@-webkit-keyframes sky_background {
    0% {
        background: #007fd5;
        color: #007fd5
    }
    50% {
        background: #000;
        color: #a3d9ff
    }
    100% {
        background: #007fd5;
        color: #007fd5
    }
}


@-webkit-keyframes cloud_one {
    0% {
        left: 0
    }
    100% {
        left: -200%
    }
}

@-webkit-keyframes cloud_two {
    0% {
        left: 0
    }
    100% {
        left: -200%
    }
}

@-webkit-keyframes cloud_three {
    0% {
    left: 0
    }
    100% {
        left: -200%
    }
}

@-moz-keyframes sky_background {
    0% {
        background: #007fd5;
        color: #007fd5
    }
    50% {
        background: #000;
        color: #a3d9ff
    }
    100% {
        background: #007fd5;
        color: #007fd5
    }
}


@-moz-keyframes cloud_one {
    0% {
        left: 0
    }
    100% {
        left: -200%
    }
}

@-moz-keyframes cloud_two {
    0% {
        left: 0
    }
    100% {
        left: -200%
    }
}

@-moz-keyframes cloud_three {
    0% {
        left: 0
    }
    100% {
        left: -200%
    }
}