Enqueue jQuery UI CSS Files

<?php
function theme_enqueue_styles() {
    // Enqueue jQuery UI themed styles.
    wp_enqueue_style( 'jquery-ui-redmond-core', 'https://cdnjs.cloudflare.com/ajax/libs/jqueryui/1.12.1/themes/redmond/jquery-ui.min.css', array(), null );
    wp_enqueue_style( 'jquery-ui-redmond-theme', 'https://cdnjs.cloudflare.com/ajax/libs/jqueryui/1.12.1/themes/redmond/theme.min.css', array(), null );
}
add_action( 'wp_enqueue_scripts', 'theme_enqueue_styles' );