Theming

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

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 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

init.lua

lua

local inline_css = [[
    window {
        background-color: transparent;
    }
]]

App:start({
    css = inline_css,
    css = "/path/to/style.css",
    css = "./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

lua

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.

lua

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

lua

App:apply_css([[
    window {
        background-color: transparent;
    }
]])

lua

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:reset_css or by passing true as a second parameter to App:apply_css.

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 Fedora Ubuntu

sudo pacman -Syu dart-sass

npm install -g sass # not packaged on Fedora

npm install -g sass # not packaged on Ubuntu

init.lua

lua

local scss = "./style.scss"
local css = "/tmp/style.css"

astal.exec(string.format("sass %s %s", scss, css))

App:start({
    css = css,
})

Theming ​

From file at startup ​

Css Property on Widgets ​

Apply Stylesheets at Runtime ​

Inspector ​