Hi,

You can add more this code to Customize > Custom CSS to do that:

.penci-body-single-style-8 .penci-move-title-above:after, 
.penci-body-single-style-5 .penci-move-title-above:after, 
.penci-body-single-style-6 .penci-move-title-above:after, 
.penci-body-single-style-7 .penci-move-title-above:after{ opacity: 0.4; }

Change value 0.4 to any value as you want. Values between 0 - 1

Change it to 0 if you want to remove the gradient.

Best Regards,

PenciDesign