Duplicate this shape, and select both layers in your layer palette.

复制该形状，在图层面板中选择这些图层。

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Double click on Background in the Layer Palette and a New Layer dialog box will appear.

在图层面板中双击背景层，然后会弹出一个层属性对话框。

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Now select Gradient Tool from the layer palette, make sure that default colors are selected (black and white you can activate them simply by pressing D on your keyboard).

选择渐变工具，保持默认颜色（黑色为前景色，白色为背景色），你可以简单的点击工具栏上面的小图标快速设置。

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