Enqueue styles in Gutenberg only if the blocks are used on the post/page

functions.php

<?php

    add_action('enqueue_block_assets', 'maybe_enqueue_scripts_and_styles' );

    function maybe_enqueue_scripts_and_styles() {

          // Map blockname with CSS filename
          $styles = array(
              "basic" => "basic"
          );

          // Extend with post types you use gutenberg on
          if( !is_admin() && is_singular( array( 'post' ) ) ) {

              $post = get_post();

              if ( gutenberg_content_has_blocks( $post->post_content ) ) {

                  $blocks = gutenberg_parse_blocks( $post->post_content );

                  foreach( $blocks AS $block ) {

                      // If you use ACF to register blocks, remove the acf prefix
                      $blockname = str_replace('acf/', '', $block['blockName']);

                      if( array_key_exists( $blockname, $styles ) ) {

                          $filename = $styles[ $blockname ];

                          wp_enqueue_style( "block-{$blockname}-css", get_stylesheet_directory_uri()."/css/blocks/{$filename}.css"  );
                      }
                  }
              }
          }

          // Enqueue everything in the admin view
          if( is_admin() ) {

              foreach( $styles AS $blockname => $style ) {
                  wp_enqueue_style( "block-{$blockname}-css", get_stylesheet_directory_uri()."/css/blocks/{$style}.css"  );
              }

          }

      }