There are several ways to center a div using CSS. For example, to center a div horizontally, you might use a flexbox with justify-content, like this:
```css
.center {
    display: flex;
    justify-content: center;
}
```

To center a div vertically, you can use align-items like so instead:
```css
.center {
    display: flex;
    align-items: center;
}
```

You can also align both, of course, like so:
```css
.center {
    display: flex;
    align-items: center;
    justify-content: center;
}
```
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