Try enqueuing via add_editor_style.

seedlet/classes/class-seedlet-custom-colors.php

@@ -265,7 +265,6 @@ class Seedlet_Custom_Colors {
 	 * Editor custom color variables.
 	 */
 	function seedlet_editor_custom_color_variables() {
-		wp_enqueue_style( 'seedlet-editor-variables', get_template_directory_uri() . '/assets/css/variables-editor.css', array(), wp_get_theme()->get( 'Version' ) );
 		if ( 'default' !== get_theme_mod( 'custom_colors_active' ) ) {
 			wp_add_inline_style( 'seedlet-editor-variables', $this->seedlet_generate_custom_color_variables( 'editor' ) );
 		}

seedlet/functions.php

@@ -109,6 +109,7 @@ if ( ! function_exists( 'seedlet_setup' ) ) :
 		// Enqueue editor styles.
 		add_editor_style( array(
 			seedlet_fonts_url(),
+			'./assets/css/variables-editor.css',
 			'./assets/css/style-editor.css'
 		) );