Stuck at this project

https://codepen.io/arunshetty/pen/ExvVjvg. hello, when I run his program I’m getting some error. I’m getting confused between css and html too. please check this and guide me to complete the challenge, with neat look.

When a test fails click the red button to see which test(s) are failing and text to help you correct the issue.
Be sure and read more than just the first line of the failing message. The ability to read and comprehend error messages is a skill you’ll need to acquire as a developer. Ask questions on what you don’t understand.

The first failing test message says;

 Within the "img-div" element, I should see either a <figcaption> or <div> element with a corresponding id="img-caption" that contains textual content describing the image shown in "img-div".
expected null to not equal null AssertionError: expected null to not equal null

Do you understand what the test is looking for?

On a side note, do not use style tags in the CSS editor. They are HTML tags and would not appear in CSS. It will cause problems.
The CSS editor in codepen is equivalent to an external stylesheet.

Thanks.
And yes I’m very much confused between HTML and CSS. I thought only chapter one in FCC is HTML, how can I understand them now???

At the very beginning, before the lessons start it says, “In this Responsive Web Design Certification, you’ll learn the languages that developers use to build webpages: HTML (Hypertext Markup Language) for content, and CSS (Cascading Style Sheets) for design.”
I’m a little confused as to what you mean by “chapter one”.

Simply put, HTML (HyperText Markup Language) is a descriptive language that specifies webpage structure, CSS (Cascading Style Sheets) is a declarative language that controls how webpages look in a browser.

I’d say maybe revisit the lessons to understand the difference between the two. Don’t rush through the lessons, learning to write code is a marathon, not a sprint.

okay I will go through all chapters once again. But what I understood now is structure and some basic style of text can be done by html. all other visuals in background is done by css. I’m a right?