hjkl-css

Parser + AST for a CSS subset used to drive declarative UI styling.

Part of the hjkl monorepo — a vim-modal editor in Rust.

Toolkit-agnostic. Pair with hjkl-css-floem to map onto floem views.

Supported subset

Selectors: type (label), class (.prompt), pseudo-class (:hover, :focus, :active, :disabled, :selected), and AND-combinations on a single simple selector (button.primary:hover). Selector lists (.a, .b) honoured. Combinators supported: descendant ( ), child (>), adjacent sibling (+), general sibling (~).
Properties (31 known): color, background-color, width, height, flex-basis, padding, margin, gap, row-gap, column-gap, display, flex-direction, align-items, justify-content, flex-grow, flex-shrink, border, border-top, border-right, border-bottom, border-left, border-width, border-color, border-top-color, border-right-color, border-bottom-color, border-left-color, border-radius, outline, font-family, font-size, font-weight, font-style, text-align, line-height. Unknown properties are silently dropped per the lenient-parsing posture.
Values: hex colors (#rgb, #rrggbb, #rrggbbaa), rgb() / rgba() functions, named colors (CSS Level 1), lengths in px / % / unitless (treated as px), auto keyword, unitless numbers, font-family lists, border shorthand (<width> <style> <color>).
Cascade: standard specificity (classes/pseudo = 10, type = 1); !important boost; CSS source-order tie-break (rule index, then in-rule declaration index).

Usage

use hjkl_css::{parse, Node, Value, Color};

let sheet = parse(r#"
    label { color: #ccc; padding: 4px 8px; }
    .prompt { color: #21d1d3; }
    .row:hover { background-color: rgba(0, 0, 0, 0.2); }
"#).expect("stylesheet parses");

let target = Node { element: "label", classes: &["prompt"] };
let style = sheet.resolve(&target, &[], &[], None);
assert_eq!(
    style.get("color"),
    Some(&Value::Color(Color::rgb(0x21, 0xd1, 0xd3))),
);

resolve takes the target node, its ancestors (root → parent, exclusive of target), its previous siblings (oldest → immediately preceding, exclusive of target), and the active pseudo-class. Pass empty slices for top-level views with no hierarchy.

ResolvedStyle::iter() yields properties in CSS source order, so adapters that apply properties sequentially get spec-correct shorthand/longhand override semantics.

Documentation

docs.rs/hjkl-css

Contributing

See the monorepo CONTRIBUTING guide.

License