# Theming

Since the widget toolkit is **GTK3** theming is done with **CSS**.

- [CSS tutorial](https://www.w3schools.com/css/)
- [GTK CSS Overview wiki](https://docs.gtk.org/gtk3/css-overview.html)
- [GTK CSS Properties Overview wiki](https://docs.gtk.org/gtk3/css-properties.html)

:::warning GTK is not the web
While most features are implemented in GTK,
you can't assume anything that works on the web will work with GTK.
Refer to the [GTK docs](https://docs.gtk.org/gtk3/css-overview.html)
to see what is available.
:::

So far every widget you made used your default GTK3 theme.
To make them more custom, you can apply stylesheets to them.

## From file at startup

You can pass a path to a file or css as a string in `App.start`

:::code-group

```ts [app.ts]
const inlineCss = `
    window {
        background-color: transparent;
    }
`

App.start({
    css: inlineCss,
    css: "./style.css",
    css: "/path/to/style.css",
})
```

:::

:::warning
When using relative paths, for example `./style.css` keep in mind that they
will be relative to the current working directory.
:::

## Css Property on Widgets

```ts
Widget.Label({
    css: "color: blue; padding: 1em;",
    label: "hello",
})
```

:::info
The `css` property of a widget will not cascade to its children.
:::

## Apply Stylesheets at Runtime

You can apply additional styles at runtime.

```ts
App.apply_css("/path/to/file.css")
```

```ts
App.apply_css(`
window {
    background-color: transparent;
}
`)
```

```ts
App.reset_css() // reset if need
```

:::warning
`App.apply_css` will apply on top of other stylesheets applied before.
You can reset stylesheets with `App.resetCss`
:::

## Inspector

If you are not sure about the widget hierarchy or any CSS selector,
you can use the [GTK inspector](https://wiki.gnome.org/Projects/GTK/Inspector)

```sh
# to bring up the inspector run
astal --inspector
```

## Using SCSS

Gtk's CSS only supports a subset of what the web offers.
Most notably nested selectors are unsupported by Gtk, but this can be
workaround by using preprocessors like [SCSS](https://sass-lang.com/).

:::code-group

```sh [<i class="devicon-archlinux-plain"></i> Arch]
sudo pacman -Syu dart-sass
```

```sh [<i class="devicon-fedora-plain"></i> Fedora]
npm install -g sass # not packaged on Fedora
```

```sh [<i class="devicon-ubuntu-plain"></i> Ubuntu]
npm install -g sass # not packaged on Ubuntu
```

:::

:::code-group

```ts [app.ts]
import { exec } from "astal/process"

exec("sass", "./style.scss", "/tmp/style.css")

App.start({
    css: "/tmp/style.css",
    main() {},
})
```

:::

:::tip
You could also transpile scss into css using a bundler
and simply passing the path of the resulting css file to `css`.
:::