This in a bootstrap library remotely loaded. To override it, got includes/templates/bootstrap/css folder and rename dist-site_specific_styles.php file to site_specific_styles.php. Then edit this file and add this between the <style> and </style> tags:
Code:
.card-deck .card {
margin-right: 15px;
margin-left: 15px;
}
Or this, depending on what part you want to change:
Code:
.col {
padding-right: 15px;
padding-left: 15px;
}
Then adjust numbers as you like. Be careful that theses changes are site wise.