CSS Using Top Position Negative figures ? Is this normal or a hack?

I have a couple of Div's with background images and the top one has a curve.

I need to just the bottom one with the top so I was thinking of using:

top: -39px;
width: 260px;

Is this use ok or is 开发者_运维技巧this considered a hack ?

Thanks

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It is completely fine and normal and common and not a hack to use negative values.