It's my first time using Zurb Foundation for a web project. However, I'm not sure whether to override their styles with my own on a separate stylesheet or directly edit `foundation.css`.

For example this is their nav css (inside `foundation.css`):

```
.nav-bar {
    background: #4D4D4D;
    height: 40px;
    margin-left: 0;
    margin-top: 20px;
    padding: 0;
}

```

If I want to change the `background` and `margin-top`, do I directly edit `.nav-bar` from `foundation.css` or create my own stylesheet (put a `style.css` below `foundation.css`) and override it like so:

```
.nav-bar {
    background: #999;
    margin-top: 0;
}

```

Is this good practice? If not, what would be the best way to go about it?