Below is the full code to include the editor style in a common way.
<?php
function my_theme_add_editor_styles() {
add_editor_style( 'custom-editor-style.css' );
}
add_action( 'admin_init', 'my_theme_add_editor_styles' );
?>
When you are adding the custom editor style, you need to use admin_init
hook which is triggered only when you are inside the admin panel. So the stylesheet will not load in the front end and is limited to admin dashboard.