custom-style.php for a child theme for Nirvana

Hello folks,

First of all, thanks for the great Nirvana theme!

I have a question about the cryout-columns feature on the Nirvana Presentation Page.
I’m using a child theme for slight css modifications.
I would like to adjust the gray overlay behaviour from the cryout-columns when hit with the mouse cursor (i.e. change the value of the alpha channel in the rgba values). It now changes to darker grey, but I want it to change to totally transparant. I found out the alpha value is in the file: includes/custom-styles.php in the parents template directory, coded as:

.coldisplay1 .column-image-inside { background: rgba(<?php echo esc_html(cryout_hex2rgb($nirvana_fpslidercaptionbg)); ?>,0.3); }
.coldisplay1 .column-image-inside:hover { background: rgba(<?php echo esc_html(cryout_hex2rgb($nirvana_fpslidercaptionbg)); ?>,0.0); }

But i would like to use the modified values in a custom-styles.php file in the directory of the child-theme. Is this possible, and do I have to keep the same hiearchy as the parents theme?

The website is: http://www.acupunctuurhaarlem.nl

Thanks in advance for help!