Starting with Photoshop CS6, you’re able to apply layer styles to a group. You can do so by double-clicking on the right side of the group in the layers panel.
If you’re on an older version, you can still apply layer styles to a group. First convert the group into a “Smart Object” (by right-clicking on the group, then choosing “Convert to Smart Object” from the Layers panel’s flyout menu), then double-clicking to the right of the group to bring up the layer style panel.
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