CSS

• Version: 1.4.0

• Path: source/lexbor/css

• Base Includes: lexbor/css/css.h

• Examples: examples/lexbor/css

• Specification: CSS

Overview

CSS itself is a modular system. Unlike a single monolithic specification, CSS is defined as a collection of independent modules, each covering a specific aspect of styling: syntax, selectors, colors, layout, fonts, text, and many others. Each CSS module has its own specification, its own level (version), and evolves at its own pace. The W3C actively develops and extends these modules, so the CSS landscape is constantly growing.

The lexbor CSS module mirrors this modular approach. It is a CSS parser that processes CSS text — stylesheets, individual rules, declarations, selectors, and values — and builds corresponding in-memory data structures. Support for CSS specification modules is being actively developed; new modules and properties are added regularly.

Important: This module handles parsing only. It builds CSS data structures (rule trees, selector lists, declaration lists) from CSS text. If you need to find HTML elements matching CSS selectors, see the Selectors module documentation.

Key Features

• Specification Compliant — implements CSS Syntax Module Level 3

• CSS Selectors Level 4 — full parsing support for CSS Selectors

• Modular Design — parser, selectors, properties, and at-rules are separate subsystems

• Stylesheet Parsing — parses complete CSS stylesheets into a rule tree (CSSOM)

• Property Parsing — parses 100+ CSS properties with typed values

• Serialization — serialize any CSS structure back to text

• Error Logging — detailed parse error reporting

• Memory Efficient — shared memory pools, parser reuse

Quick Start

Parse a Stylesheet

#include <lexbor/css/css.h>

static lxb_status_t
callback(const lxb_char_t *data, size_t len, void *ctx)
{
    printf("%.*s", (int) len, (const char *) data);
    return LXB_STATUS_OK;
}

int main(void)
{
    const lxb_char_t css[] = "div { color: red; font-size: 16px; }";

    /* Create and initialize the parser */
    lxb_css_parser_t *parser = lxb_css_parser_create();
    lxb_status_t status = lxb_css_parser_init(parser, NULL);
    if (status != LXB_STATUS_OK) {
        return EXIT_FAILURE;
    }

    /* Create a stylesheet object */
    lxb_css_stylesheet_t *sst = lxb_css_stylesheet_create(NULL);
    if (sst == NULL) {
        lxb_css_parser_destroy(parser, true);
        return EXIT_FAILURE;
    }

    /* Parse CSS into the stylesheet */
    status = lxb_css_stylesheet_parse(sst, parser, css, sizeof(css) - 1);
    if (status != LXB_STATUS_OK) {
        lxb_css_stylesheet_destroy(sst, true);
        lxb_css_parser_destroy(parser, true);
        return EXIT_FAILURE;
    }

    /* Serialize the rule tree back to text */
    lxb_css_rule_serialize(sst->root, callback, NULL);
    printf("\n");

    /* Clean up */
    lxb_css_stylesheet_destroy(sst, true);
    lxb_css_parser_destroy(parser, true);

    return EXIT_SUCCESS;
}

Output:

div {color: red; font-size: 16px}

CSS Specification Modules

The table below lists CSS specification modules and their support status in lexbor. The modules marked as supported have full or near-complete parsing implementation. Work on adding support for new modules is ongoing.

Supported

CSS Module	Specification	What It Covers
CSS Syntax	Level 3	Tokenization and grammar rules — the foundation for all other modules
CSS Selectors	Level 4	Selector parsing: type, class, ID, attribute, pseudo-classes, pseudo-elements, combinators
CSS Cascading and Inheritance	Level 3–4	Keywords initial, inherit, unset, revert
CSS Color	Level 4	Color values: named colors, hex, rgb(), hsl(), hwb(), lab(), lch()
CSS Values and Units	Level 4	Lengths, angles, durations, frequencies, resolutions, percentages
CSS Box Model	Level 3	width, height, margin, padding, box-sizing
CSS Flexible Box Layout	Level 1	display: flex, flex-direction, flex-wrap, justify-content, align-items, etc.
CSS Positioned Layout	Level 3	position, top, right, bottom, left, z-index
CSS Fonts	Level 4	font-family, font-size, font-weight, font-style, font-stretch
CSS Text	Level 4	text-align, text-indent, white-space, word-break, letter-spacing, line-height, etc.
CSS Text Decoration	Level 3	text-decoration, text-decoration-line, text-decoration-color, text-decoration-style
CSS Writing Modes	Level 4	writing-mode, text-orientation, direction, unicode-bidi
CSS Overflow	Level 3	overflow-x, overflow-y, text-overflow
CSS Inline Layout	Level 3	vertical-align, dominant-baseline, alignment-baseline
CSS Display	Level 3	display, visibility, order

Not Yet Supported

These modules are not yet implemented but may be added in the future:

CSS Module	Specification
CSS Grid Layout	Level 2
CSS Multi-column Layout	Level 1
CSS Transitions	Level 1
CSS Animations	Level 1
CSS Transforms	Level 2
CSS Backgrounds and Borders	Level 3
CSS Images	Level 4
CSS Shapes	Level 1
CSS Containment	Level 2
CSS Custom Properties	Level 1
CSS Scroll Snap	Level 1
CSS Conditional Rules - @media	Level 3
CSS Fonts — @font-face	Level 4
CSS Namespaces — @namespace	Level 3