Hier, wie ich das in etwa meine:
HTML-Code:
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<style>
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body { display: table-cell; vertical-align: middle; text-align: center; }
img { position: absolute; width: 100%; height: 100%; left: 0; top: 0; }
iframe { position: relative; display: inline-block; /*text-align: left;*/ }
</style>
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