This may be a question for Complianz customer support. I don't have a copy of that plugin to do any sort of testing.

You can use the CSS code. Just modify as you need and add it to the custom CSS code for the review template on the first tab.

span.wprev_totrevs {
font-size: 14px !important;
color: black;
}

Are you using the Advanced slider or the Normal? You can right-click on the arrow > inspect > and then it should show you what CSS classes are being used.

Once you have the CSS class you can overwrite it in the Custom CSS section of the review template like so...

.wprs_unslider-arrow {
width: 15px;
height: 15px;
}

https://www.google.com/recaptcha/admin/create

Make sure you use V2....

Then it should give you this...

You would need to change it to a slider. Then you get the arrows.