Layer Styles in Adobe Photoshop allow you to save off some settings for future use.
Think of when you want to apply a Bevel Emboss, Color Overlay, Drop Shadow, etc. You can save off that combo, name it and use it again later to speed things up and keep it consistent or use it as a jump-off point.
On the left, you can see the different Styles like Bevel & Emboss, Drop Shadow, Gradient Overlay, etc.
Layer Style Presets
Saving off the Styles will list them in the window. You can find them and apply them quickly.
Activate Multiple Styles with 1 Click
Take a look at all the checks on the left column. That shows all the Styles activated to create a new Style for your project.
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