Showing you how to add to or override the Redux CSS values.

addAndOverridePanelCSS.php

<?php
function addAndOverridePanelCSS() {
  wp_dequeue_style( 'redux-css' );
  wp_register_style(
    'redux-custom-css',
    'http://urltomyfile',
    array( 'farbtastic' ), // Notice redux-css is removed and the wordpress standard farbtastic is included instead
    time(),
    'all'
  );	
  wp_enqueue_style('redux-custom-css');
}
// This example assumes your opt_name is set to redux_demo, replace with your opt_name value
add_action('redux-enqueue-redux_demo', 'addAndOverridePanelCSS');

addPanelCSS.php

<?php
function addPanelCSS() {
    wp_register_style(
        'redux-custom-css',
        'http://urltomyfile',
        array( 'redux-css' ), // Be sure to include redux-css so it's appended after the core css is applied
        time(),
        'all'
    );  
    wp_enqueue_style('redux-custom-css');
}
// This example assumes your opt_name is set to redux_demo, replace with your opt_name value
add_action('redux-enqueue-redux_demo', 'addPanelCSS');

removePanelCSS.php

<?php
function removePanelCSS() {
  wp_dequeue_style( 'redux-css' );
}
// This example assumes your opt_name is set to redux_demo, replace with your opt_name value
add_action('redux-enqueue-redux_demo', 'removePanelCSS');