source: sydney/1.59/inc/editor.php

<?php

/**
 * Gutenberg support
 */

function sydney_editor_styles() {
        wp_enqueue_style( 'sydney-block-editor-styles', get_theme_file_uri( '/sydney-gutenberg-editor-styles.css' ), '', '1.0', 'all' );

        wp_enqueue_style( 'sydney-fonts', esc_url( sydney_enqueue_google_fonts() ), array(), null );


        //Dynamic styles
        $custom = '';

        //Fonts
        $body_fonts     = get_theme_mod('body_font', 'Raleway');        
        $headings_fonts = get_theme_mod('headings_font', 'Raleway');
        $custom .= ".editor-block-list__layout, .editor-block-list__layout .editor-block-list__block { font-family:" . $body_fonts . ";}"."\n";
        $custom .= ".editor-post-title__block .editor-post-title__input, .editor-block-list__layout .editor-post-title__input, .editor-block-list__layout h1, .editor-block-list__layout h2, .editor-block-list__layout h3, .editor-block-list__layout h4, .editor-block-list__layout h5, .editor-block-list__layout h6 { font-family:" . $headings_fonts . ";}"."\n";
        
        
        //H1 size
        $h1_size = get_theme_mod( 'h1_size','52' );
        if ($h1_size) {
                $custom .= ".editor-block-list__layout h1 { font-size:" . intval($h1_size) . "px; }"."\n";
        }
        //H2 size
        $h2_size = get_theme_mod( 'h2_size','42' );
        if ($h2_size) {
                $custom .= ".editor-block-list__layout h2 { font-size:" . intval($h2_size) . "px; }"."\n";
        }
        //H3 size
        $h3_size = get_theme_mod( 'h3_size','32' );
        if ($h3_size) {
                $custom .= ".editor-block-list__layout h3 { font-size:" . intval($h3_size) . "px; }"."\n";
        }
        //H4 size
        $h4_size = get_theme_mod( 'h4_size','25' );
        if ($h4_size) {
                $custom .= ".editor-block-list__layout h4 { font-size:" . intval($h4_size) . "px; }"."\n";
        }
        //H5 size
        $h5_size = get_theme_mod( 'h5_size','20' );
        if ($h5_size) {
                $custom .= ".editor-block-list__layout h5 { font-size:" . intval($h5_size) . "px; }"."\n";
        }
        //H6 size
        $h6_size = get_theme_mod( 'h6_size','18' );
        if ($h6_size) {
                $custom .= ".editor-block-list__layout h6 { font-size:" . intval($h6_size) . "px; }"."\n";
        }
        //Body size
        $body_size = get_theme_mod( 'body_size', '16' );
        if ($body_size) {
                $custom .= ".editor-block-list__block, .editor-block-list__block p { font-size:" . intval($body_size) . "px; }"."\n";
        }
        //Single post title
        $single_post_title_size = get_theme_mod( 'single_post_title_size', '36' );
        if ($single_post_title_size) {
                $custom .= ".editor-post-title__block .editor-post-title__input, .editor-block-list__layout .editor-post-title__input { font-size:" . intval($single_post_title_size) . "px; }"."\n";
        }

        //__COLORS
        //Primary color
        $primary_color = get_theme_mod( 'primary_color', '#d65050' );
        $custom .= ".editor-block-list__layout blockquote.wp-block-quote, .editor-block-list__layout .wp-block-quote:not(.is-large):not(.is-style-large) { border-color:" . esc_attr($primary_color) . "}"."\n";

        //Body
        $body_text = get_theme_mod( 'body_text_color', '#47425d' );
        $custom .= ".editor-block-list__layout, .editor-block-list__layout .editor-block-list__block { color:" . esc_attr($body_text) . "}"."\n";

        //Small screens font sizes
        $custom .= "@media only screen and (max-width: 780px) { 
                h1 { font-size: 32px;}
                h2 { font-size: 28px;}
                h3 { font-size: 22px;}
                h4 { font-size: 18px;}
                h5 { font-size: 16px;}
                h6 { font-size: 14px;}
        }" . "\n";

        
        //Output all the styles
        wp_add_inline_style( 'sydney-block-editor-styles', $custom );   

}
add_action( 'enqueue_block_editor_assets', 'sydney_editor_styles' );