Can't get my CSS to show

I've been trying to start building a website for the first time using CodeIgniter, and I can't seem to get my css to load. I've looked on a lot of sites and have tried to find the answer, but none seem to work so far.

Code:

<link href="<?php echo base_url('assets/css/style.css'); ?>" rel="stylesheet">

It directs to the location of the css file but when I press F12 to see the error, it says Error 404 not found.
My css folder is located here:
C:\xampp\htdocs\CI4\assets\css

Any help is appreciated
Thanks.