WooCommerce loads three core CSS style sheets on every page and post when installed on a WordPress site. You can save a bit of page load time here by removing the styles and scripts from pages and content that do not need it .
Here is how you can load these files a bit differently so they appear only on the pages you need, speeding up page load time for non-Woocommerce content.
These are loaded from /wp-content/plugins/woocommerce/assets/css/
Woo have made a filter available to remove all 3 or remove individual ones.
You can do this and just add your own CSS style
This is great but it still loads on every page, if you keep your WooCommerce on the default pages you can conditionally load the CSS file.
Here all the Woo styles and scripts are removed by hooking into ‘template_redirect’ the last hook before the page loads and removing the initial Woo add_action of all styles and scripts.