With the new layer implementation, Capture One now provides the ability to edit more quickly, with more precision than before, and it also makes for your adjustments to be altered with ease at any time. 

Within the Capture One Layers section you will find the Opacity slider, and this, in effect, works as it does in Photoshop. You just create a new filled layer, add a PixaFOTO style, and choose how much of the preset you want to apply. 

How to Change Opacity of Capture One Styles - VIDEO