设置一个负值的y轴偏移转将阴影转移到顶部。

Set a negative value for y-offset to shift the shadow to the top.

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设置一个负值的x轴偏移将阴影转移到左侧。

Set a negative value for x-offset to shift the shadow to the left.

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盒阴影的结构和text - shadow相同，x轴偏移，y轴偏移，模糊，颜色。

The structure for box shadow is same as the text-shadow property: x-offset, y-offset, blur, and color.

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