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How do you create a box filled with a color with HTML / CSS?
Yes, please!
Here's an example code snippet for creating a box with a blue background color:

```html
<div class="blue-box"></div>
```

```css
.blue-box {
  background-color: blue;
  width: 100px;
  height: 100px;
}
```

This will create a box with a class of "blue-box" and set its background color to blue.