Animate image like it's moving from right to left

.container {
    width: 50%;
    margin: 0 auto;
    text-align: center;
}

#clouds{
    padding: 100px 0;
    background: #3598dc;
    background: -webkit-linear-gradient(top, #3598dc 0%, #fff 100%);
    background: -linear-gradient(top, #3598dc 0%, #fff 100%);
    background: -moz-linear-gradient(top, #3598dc 0%, #fff 100%);
}

.cloud {
    width: 200px; height: 60px;
    background: #fff;
    border-radius: 200px;
    -moz-border-radius: 200px;
    -webkit-border-radius: 200px;
    position: relative;
}

.cloud:before, .cloud:after {
    content: '';
    position: absolute;
    background: #fff;
    width: 100px; height: 80px;
    position: absolute; top: -15px; left: 10px;

    border-radius: 100px;
    -moz-border-radius: 100px;
    -webkit-border-radius: 100px;
    -webkit-transform: rotate(30deg);
    transform: rotate(30deg);
    -moz-transform: rotate(30deg);
}

.cloud:after {
    width: 120px; height: 120px;
    top: -55px; left: auto; right: 15px;
}

#character{
    margin-top: -120px;
    background:url(http://i.imgur.com/Zjsbcni.png);
    width: 84px;
    height: 126px;
    animation: walk 1.0s steps(6) infinite;
    margin-left: 425px;
}

#flooring {
    height: 39px;
    background-image: url(http://i.imgur.com/usFekrp.png);
    animation: movefloor 20s linear infinite;
    overflow: hidden;
}

@keyframes movefloor {
    0% {margin-left: 1000px;}
    100% {margin-left: -1000px;}
}

@keyframes walk {
    from { background-position: 0px; }
    to { background-position: -500px; }
}

.x1 {
    -webkit-animation: moveclouds 15s linear infinite;
    -moz-animation: moveclouds 15s linear infinite;
    -o-animation: moveclouds 15s linear infinite;
}

.x2 {
    left: 200px;
    -webkit-transform: scale(0.6);
    -moz-transform: scale(0.6);
    transform: scale(0.6);
    opacity: 0.6; /*opacity proportional to the size*/

    -webkit-animation: moveclouds 25s linear infinite;
    -moz-animation: moveclouds 25s linear infinite;
    -o-animation: moveclouds 25s linear infinite;
}

.x3 {
    left: 252px;
    top: -200px;
    -webkit-transform: scale(0.8);
    -moz-transform: scale(0.8);
    transform: scale(0.8);
    opacity: 0.8; /*opacity proportional to the size*/

    -webkit-animation: moveclouds 20s linear infinite;
    -moz-animation: moveclouds 20s linear infinite;
    -o-animation: moveclouds 20s linear infinite;
}


@-webkit-keyframes moveclouds {
    0% {margin-left: 1000px;}
    100% {margin-left: -1000px;}
}
@-moz-keyframes moveclouds {
    0% {margin-left: 1000px;}
    100% {margin-left: -1000px;}
}
@-o-keyframes moveclouds {
    0% {margin-left: 1000px;}
    100% {margin-left: -1000px;}
}

<div class="container">
    <div id="clouds">
        <div class="cloud x1"></div>
        <div class="cloud x2"></div>
        <div class="cloud x3"></div>
        <div class="cloud x4"></div>
        <div class="cloud x5"></div>
    </div>
    <div id="character"></div>
    <div id="flooring"></div>
</div>