Add Custom CSS in Redux Framework
<?php
add_action('wp_head' , 'display_custom_css');
function display_custom_css()
{?>
<style>
<?php $options = get_option('redux_demo'); ?>
<?php echo $options['opt-ace-editor-css']; ?>
</style>
<?php }
?>
Now you can write a custom css for your pages or posts. Just write in the editor and call those classes/ ids in the posts/pages