[html] How to put two divs side by side

http://jsfiddle.net/kkobold/qMQL5/

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#header {_x000D_
    width: 100%;_x000D_
    background-color: red;_x000D_
    height: 30px;_x000D_
}_x000D_
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#container {_x000D_
    width: 300px;_x000D_
    background-color: #ffcc33;_x000D_
    margin: auto;_x000D_
}_x000D_
#first {_x000D_
    width: 100px;_x000D_
    float: left;_x000D_
    height: 300px;_x000D_
        background-color: blue;_x000D_
}_x000D_
#second {_x000D_
    width: 200px;_x000D_
    float: left;_x000D_
    height: 300px;_x000D_
    background-color: green;_x000D_
}_x000D_
#clear {_x000D_
    clear: both;_x000D_
}
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<div id="header"></div>_x000D_
<div id="container">_x000D_
    <div id="first"></div>_x000D_
    <div id="second"></div>_x000D_
    <div id="clear"></div>_x000D_
</div>
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