change slideout exit icon

Hi there,

Are you using font icons or SVG icons in "Customize > General"?

Let me know :)

I'm using SVG icons.

You could try this:

add_filter( 'generate_svg_icon, function( $output, $icon ) {
    if ( 'pro-close' === $icon ) {
        $svg = 'Your SVG HTML';
    }

    if ( $svg ) {
        $output = sprint(
            '<span class="gp-icon %1$s">
                %2$s
            </span>',
            $icon,
            $svg
        );
    }

    return $output;
}, 15, 2 );

I added this code and it breaks my site. What does that 15, 2 means?

15 is the priority of the function, and 2 is the number of the arguments required by the filter.
Where did you add the code ? And what error did it produce?