ironbar/docs/Styling guide.md

Ironbar ships with no styles by default, so will fall back to the default GTK styles.

To style the bar, create a file at `~/.config/ironbar/style.css`.

Style changes are hot-loaded so there is no need to reload the bar.

Since the bar is GTK-based, it uses [GTK's implementation of CSS](https://docs.gtk.org/gtk3/css-overview.html),
which only includes a subset of the full web spec (plus a few non-standard properties).

The below table describes the selectors provided by the bar itself.
Information on styling individual modules can be found on their pages in the sidebar.

| Selector            | Description                                |
|---------------------|--------------------------------------------|
| `.background`       | Top-level window.                          |
| `#bar`              | Bar root box.                              |
| `#bar #start`       | Bar left or top modules container box.     |
| `#bar #center`      | Bar center modules container box.          |
| `#bar #end`         | Bar right or bottom modules container box. |
| `.container`        | All of the above.                          |
| `.widget-container` | The `EventBox` wrapping any widget.        |
| `.widget`           | Any widget.                                |
| `.popup`            | Any popup box.                             |

Every widget can be selected using a `kebab-case` class name matching its name. 
You can also target popups by prefixing `popup-` to the name. For example, you can use `.clock` and `.popup-clock` respectively.

Setting the `name` option on a widget allows you to target that specific instance using `#name`. 
You can also add additional classes to re-use styles. In both cases, `popup-` is automatically prefixed to the popup (`#popup-name` or `.popup-my-class`).

You can also target all GTK widgets of a certain type directly using their name. For example, `button:hover` will select the hover state on *all* buttons.
These names are all lower case with no separator, so `MenuBar` -> `menubar`.

GTK CSS does not support custom properties, but it does have its own custom `@define-color` syntax which you can use for re-using colours:

```css
@define-color color_bg #2d2d2d;

box, menubar {
    background-color: @color_bg;
}
```