> For the complete documentation index, see [llms.txt](https://docs.idew.org/code-internet-of-things/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.idew.org/code-internet-of-things/tutorials/create-security-system/4.7-web-app-html.md).
# D-7 Web App HTML
Next, you'll create a web app that will interact with your Smart Security device through Particle Cloud.
Your web app will consist of an HTML file named`index.html`, a CSS file named `style.css`, and a JavaScript file named `script.js`.
Remember that Particle Build is only used to code your Photon device app. You'll need to use a different code editor to create the HTML, CSS, and JS files for your web app. Consult your teacher to determine which code editor will be most appropriate to use for your web app files.
## Add Starter HTML
[Copy this starter HTML for your web app](https://docs.idew.org/code-internet-of-things/references/web-app#html), and paste it into a **blank** HTML file named `index.html`.
The starter HTML contains blank lines where you'll add custom HTML for your specific web app.
## Add Custom HTML
Copy this HTML, and paste it into the blank lines **within** the `` of your starter HTML code:
```markup
Smart Security System
Motion Detected
```
{% hint style="success" %}
**COPY CODE:** When using this IoT code guidebook, you can copy a code block simply by clicking the **copy icon** displayed in the upper right of the code block.
{% endhint %}
## Preview Web App
If you preview the web app at this point, it's very plain (because there's no CSS in the `style.css` file) and it doesn't function yet (because there's no JS in the `code.js` file).
---
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