​x
 
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<!DOCTYPE html>
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<title>My Example</title>
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<style>
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    #unique {
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        background-image: url('/pix/samples/bg2.png');
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    }
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    div {
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        width: 20vw;
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        margin: 2vw;
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        padding: 3vw;
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        border: solid;
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    }
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</style>
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​
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<div id="unique">ID</div>
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<div>No ID</div>
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​
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<p>Note that only one element on the page can use a given ID. To style multiple elements, use a class.</p>