Theming

Since the widget toolkit is GTK theming is done with CSS.

• CSS tutorial
• GTK3 CSS Overview wiki
• GTK3 CSS Properties Overview wiki
• GTK4 CSS Overview wiki
• GTK4 CSS Properties Overview wiki

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 to see what is available.

So far every widget you made used your default GTK 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

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

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.

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

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

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

# 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.

Arch

sudo pacman -Syu dart-sass

Fedora

npm install -g sass # not packaged on Fedora

Ubuntu

npm install -g sass # not packaged on Ubuntu

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.