This code snippet injects a styled "Continue Shopping" button after the cart totals on the WooCommerce cart page. It achieves this by utilizing the `add_action` function to hook a custom function (`cart_extra_text`) to the `woocommerce_after_cart_totals` action hook.

Components:

1. Function: `cart_extra_text`
     This function is responsible for creating the button element and its styling.
     It doesn't take any arguments (`0` passed to `add_action`).

2. Styling (lines 1-21):
     The function first injects a `<style>` tag using `echo` (line 1).
     Within the `<style>` tag, it defines styles for the button element with the ID `#cart-extra-text a` (lines 3-21). Here's a breakdown of the styles:
         Lines 3-5: Set the button to display as a block-level element and occupy full width.
         Lines 6-8: Define background color (`#222222`), text color (`#FFFFFF`), and center text alignment.
         Lines 9-12: Add padding, set font size, weight, and transform text to uppercase.
         Lines 13-16: Remove underline, border, and set cursor to pointer on hover.
         Lines 17-20 (Optional): Add hover effect with a darker background color (`#FF0050`).

3. Button Creation (line 23):
     The function creates a `<div>` element with the ID `cart-extra-text` to contain the button (line 23).
     Inside the `<div>`, it creates an anchor (`<a>`) element with the following attributes:
         Text: "Continue Shopping"
         Href: Link to your desired "Continue Shopping" page (here, `https://learn.websquadron.co.uk/#join`)
         Target: Opens the link in a new tab (`_blank`)

4. Hooking the Function (line 25):
     The final line utilizes `add_action` to connect the `cart_extra_text` function to the `woocommerce_after_cart_totals` action hook.
     Parameters passed to `add_action`:
         `'woocommerce_after_cart_totals'`: The action hook triggered after cart totals are displayed.
         `'cart_extra_text'`: The name of the function to be executed.
         `10`: Priority (optional, set to 10 for execution after other functions with lower priority).
         `0`: Number of arguments the function expects (here, none).

Overall Functionality:

When the WooCommerce cart page renders, the `woocommerce_after_cart_totals` action is triggered. This calls the `cart_extra_text` function, which injects the styled button element after the cart totals. The button encourages users to continue shopping on your website.

Customization:

 You can modify the button text (line 23) and link URL to suit your needs.
 Adjust the styles within the `<style>` tag (lines 1-21) to change the button's appearance.
 The priority (`10`) passed to `add_action` can be adjusted if you need the button to display before or after other elements hooked to the same action (experiment with different values).