Why you use external link for bootstrap files

Download your css file and js file then enque like your local. Files

write the following in your code

<?php add_action( 'wp_enqueue_scripts', 'theme_enqueue_styles' ); function theme_enqueue_styles() { wp_enqueue_style( 'parent-style', get_template_directory_uri() . '/style.css' ); } function my_scripts_enqueue() { wp_register_script( 'bootstrap-js', 'https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js', array('jquery'), NULL, true ); wp_register_style( 'bootstrap-css', 'https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css', false, NULL, 'all' ); wp_enqueue_script( 'bootstrap-js' ); wp_enqueue_style( 'bootstrap-css' ); } add_action( 'wp_enqueue_scripts', 'my_scripts_enqueue' ); ?> 

it will download your file