Programming · Lesson 4 of 7
HTML, CSS, and JavaScript
Every website runs on three things. Once you understand what each does, nothing looks mysterious.
After This Lesson, You Will Be Able To
Understand the role of HTML, CSS, and JavaScript in a webpage — and modify each layer of an existing project using AI assistance.
The Three Layers of Every Website
HTML: The Structure
Think of HTML as the skeleton of a building — it defines what rooms exist and where they are, but not what they look like.
AI can generate all the HTML you need. You need to understand that `
` is a heading, `
` is a paragraph, `
CSS: The Style
AI is exceptionally good at generating CSS. You can describe what you want visually and Claude will produce the CSS. What matters is that you can identify which CSS property to ask Claude to change when something doesn't look right.
JavaScript: The Behavior
This is the most powerful and complex of the three. AI can generate JavaScript that does sophisticated things. Your job is to describe what should happen when the user does something.
How to Modify AI Code for Each Layer
Change the structure (HTML)
Ask Claude: 'Add a new section below the hero with 3 feature cards. Each card has a title, a description, and an icon.' Claude adds the HTML and you see it immediately.
Change the look (CSS)
Ask Claude: 'Change the background color to dark blue, make the heading font size larger, and add 20px padding to all sections.' Claude modifies the CSS.
Change the behavior (JavaScript)
Ask Claude: 'When the user submits the form, show an alert saying Thank you for your message and clear the form fields.' Claude adds or modifies the JavaScript.
Exercise
~10 minutes · ChatGPT or Claude
Prompt to use
I have this existing webpage: [paste your HTML file code]. I want to make the following changes: 1) Structure change: [describe what content to add or move], 2) Visual change: [describe how you want it to look differently], 3) Behavior change: [describe what should happen when the user does something]. Make each change separately and explain which technology (HTML, CSS, or JavaScript) each change touches and why.
Every website you've ever visited is built from these three things. Right-click on any webpage and click 'Inspect'. What do you see?
Key Takeaways
HTML = structure (what's on the page). CSS = style (how it looks). JS = behavior (what happens when you interact).
AI generates all three. Your job is to describe what you want clearly and know which layer to ask Claude to change.
Right-click → Inspect on any website to see its HTML, CSS, and JS. This is how you learn what's possible.
You never need to write these from scratch. Understanding what they do makes you a more effective director of AI.
Inspect your favorite website and identify the three layers.
Open a website you use regularly. Right-click anywhere and select 'Inspect' (Chrome/Firefox). You'll see the HTML panel on the left. Click the Elements tab to explore the structure. Click the Styles panel to see the CSS. This is not intimidating — you're just reading. Take 10 minutes to explore, then ask Claude to explain anything that confuses you.
Next Lesson
Working with APIs
Programming · Lesson 5 of 7 · 10 min