Crate `strata_style`: CSS Engine, Cascade Solver & Tailwind JIT

The strata_style crate provides a zero-dependency styling engine for Project Strata. It encompasses a CSS parser, a W3C-compliant specificity and cascade solver, a high-throughput Tailwind CSS v3/v4 JIT compiler, a mathematical calc() AST engine, and a cubic-bezier @keyframes animator.

Architectural Systems

text

┌────────────────────────────────────────────────────────────────────────┐
│                              strata_style                              │
└───────┬──────────────┬──────────────┬──────────────┬─────────────┬─────┘
        │              │              │              │             │
        ▼              ▼              ▼              ▼             ▼
┌──────────────┐┌──────────────┐┌──────────────┐┌─────────────┐┌─────────┐
│  parser.rs   ││specificity.rs││ tailwind.rs  ││  calc.rs    ││keyframe.│
│ CSS Lexer &  ││cascade.rs    ││ Tailwind JIT ││ calc() AST  ││Cubic-   │
│ Declarations ││ CascadeSolver││ Modifiers    ││ Evaluator   ││ Bezier  │
└──────────────┘└──────────────┘└──────────────┘└─────────────┘└─────────┘

CSS Lexer & Stylesheet Parser (`parser`)

The CSS parser processes standard stylesheets, extracts selectors and declaration blocks, strips comments, and produces typed AST elements with zero external dependencies.

rust

pub struct Declaration {
    pub property: String,
    pub value: String,
    pub important: bool,
}

pub struct StyleRule {
    pub selectors: Vec<Selector>,
    pub declarations: Vec<Declaration>,
}

pub struct StyleSheet {
    pub rules: Vec<StyleRule>,
}

Parsing Pipeline

Comment Stripping: Removes standard block comments (/* ... */).
Selector Tokenization: Identifies tag, class (.), ID (#), and pseudo-class (:hover, :focus) tokens.
Declaration Block Parsing: Decodes key-value pairs, stripping whitespace and detecting !important markers.

rust

use strata_style::parser::StyleSheet;

let css = r#"
    .telemetry-card {
        background-color: #18181b;
        padding: 16px;
        border-radius: 8px;
    }
    .telemetry-card:hover {
        background-color: #27272a !important;
    }
"#;

let stylesheet = StyleSheet::parse(css).expect("Valid CSS");
assert_eq!(stylesheet.rules.len(), 2);

Specificity & Cascade Solver (`specificity`, `cascade`)

The cascade solver evaluates conflicting CSS declarations per the W3C Selectors Level 4 specification.

The Specificity 4-Tuple

Specificity is represented as a lexicographically ordered 4-tuple:

$$\mathbf{S} = (I, A, B, C)$$

$I$ (inline): Set to 1 for inline style="..." attributes, 0 otherwise.
$A$ (id_count): Number of ID selectors (#telemetry-header).
$B$ (class_count): Number of class selectors (.active), attribute selectors ([data-mode]), and pseudo-classes (:hover).
$C$ (type_count): Number of tag selectors (div, span) and pseudo-elements.

rust

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Default, Hash)]
pub struct Specificity {
    pub inline: u8,
    pub id_count: u16,
    pub class_count: u16,
    pub type_count: u16,
}

Because Specificity derives Ord, comparing two rules follows CSS priority naturally:

$$(0, 1, 0, 0) > (0, 0, 12, 4) \quad \implies \text{ID beats 12 classes}$$

Cascade Resolution Algorithm (`CascadeSolver::resolve`)

When determining the computed style of an element, CascadeSolver executes a multi-step resolution pipeline:

text

 1. Base Initialization (Inherit from parent ComputedStyle or default)
                            │
                            ▼
 2. Rule Matching (Collect matching rules from stylesheets)
                            │
                            ▼
 3. Inline Styles (Inject inline style declarations with Specificity::INLINE)
                            │
                            ▼
 4. Priority Ordering:
    Sort candidates by: (!important, Specificity, Source Order)
                            │
                            ▼
 5. Property Application (Mutate target ComputedStyle in sorted order)

rust

use strata_style::cascade::CascadeSolver;
use strata_style::selector::PseudoState;
use strata_style::types::ComputedStyle;

let parent_style = ComputedStyle::default();
let mut pseudo = PseudoState::default();
pseudo.is_hovered = true;

let computed = CascadeSolver::resolve(
    "div",
    &["telemetry-card"],
    Some("node-panel"),
    Some("border-width: 1px;"),
    &[&stylesheet],
    Some(&parent_style),
    &pseudo,
);

Tailwind CSS v3/v4 JIT Engine (`tailwind`)

TailwindEngine provides zero-regex, fast compilation of utility classes directly into ComputedStyle properties.

Supported Utility Categories

Category	Tailwind Classes	Resolved `ComputedStyle`
Display	`flex`, `grid`, `block`, `inline-flex`, `hidden`	`Display::Flex`, `Display::Grid`, `Display::None`
Flexbox	`flex-row`, `flex-col`, `items-center`, `justify-between`, `gap-4`	`flex_direction`, `align_items`, `justify_content`, `gap`
Grid	`grid-cols-3`, `grid-rows-2`, `col-span-2`	`grid_template_columns`, `grid_column_span`
Sizing	`w-full`, `h-64`, `max-w-md`, `min-h-screen`	`Dimension::Percent(100.0)`, `Dimension::Px(256.0)`
Colors	`bg-neutral-900`, `text-cyan-400`, `border-emerald-500`	Hex lookup in pre-baked Tailwind palette
Typography	`text-xs`, `text-lg`, `font-mono`, `font-bold`	`font_size: 12.0`, `font_weight: 700`
Borders	`rounded-lg`, `border`, `border-2`	`border_radius: 8.0`, `border_width: 1.0`

Modifier Support (`resolve_classes_with_state`)

Modifiers conditionally activate utilities based on runtime element states:

hover:: Active when cursor hovers over the element.
focus:: Active when element possesses keyboard focus.
dark:: Active when application theme is in dark mode.

rust

use strata_style::tailwind::TailwindEngine;

let classes = "flex items-center p-4 bg-neutral-900 hover:bg-neutral-800 text-white";
let style = TailwindEngine::resolve_classes_with_state(
    classes,
    true,  // is_hovered
    false, // is_focused
    true,  // is_dark_mode
);

assert_eq!(style.padding.left, 16.0);
assert_eq!(style.padding.top, 16.0);

Mathematical `calc()` AST Engine (`calc`)

CSS requires resolving complex dimensional expressions with mixed units, such as calc(100% - 24px + 1.5rem). strata_style::calc compiles these into an expression AST and caches them via CalcId.

Expression AST Representation

rust

#[derive(Debug, Clone, PartialEq)]
pub enum CalcExpr {
    Value(Dimension),
    Add(Box<CalcExpr>, Box<CalcExpr>),
    Sub(Box<CalcExpr>, Box<CalcExpr>),
    Mul(Box<CalcExpr>, f32),
    Div(Box<CalcExpr>, f32),
}

Contextual Resolution (`CalcContext`)

Because percentages, rem, em, vw, and vh depend on external layout environments, evaluation takes a CalcContext:

rust

pub struct CalcContext {
    pub parent_size: f32,
    pub root_font_size: f32,
    pub current_font_size: f32,
    pub viewport_width: f32,
    pub viewport_height: f32,
}

rust

use strata_style::calc::{parse_calc, CalcContext};

let expr = parse_calc("100% - 32px").expect("Valid expression");
let ctx = CalcContext {
    parent_size: 1000.0,
    root_font_size: 16.0,
    current_font_size: 16.0,
    viewport_width: 1920.0,
    viewport_height: 1080.0,
};

let resolved_pixels = expr.eval(&ctx);
assert_eq!(resolved_pixels, 968.0); // 1000.0 - 32.0

Declarative Keyframe Animations (`keyframes`)

The keyframes subsystem provides cubic-bezier timing curves and timeline property interpolation for smooth 60/120 FPS transitions.

Newton-Raphson Cubic-Bezier Solver

Implements the standard parametric cubic-bezier timing function:

$$x(t) = 3(1-t)^2 t x_1 + 3(1-t) t^2 x_2 + t^3$$ $$y(t) = 3(1-t)^2 t y_1 + 3(1-t) t^2 y_2 + t^3$$

To solve for output $y$ given input time progress $x \in [0.0, 1.0]$, CubicBezier::solve executes Newton-Raphson iteration with a binary search bisection fallback for numerical stability:

rust

pub struct CubicBezier {
    pub x1: f32,
    pub y1: f32,
    pub x2: f32,
    pub y2: f32,
}

Standard easing curves are available as constants:

CubicBezier::linear(): (0.0, 0.0, 1.0, 1.0)
CubicBezier::ease(): (0.25, 0.1, 0.25, 1.0)
CubicBezier::ease_in(): (0.42, 0.0, 1.0, 1.0)
CubicBezier::ease_out(): (0.0, 0.0, 0.58, 1.0)
CubicBezier::ease_in_out(): (0.42, 0.0, 0.58, 1.0)

Animation Sampling

rust

use strata_style::keyframes::{CubicBezier, Keyframe, KeyframeAnimation, KeyframeProperty};

let anim = KeyframeAnimation::new(
    "pulse-alert",
    1.0, // 1.0 second duration
    CubicBezier::ease_in_out(),
    vec![
        Keyframe::new(0.0, vec![KeyframeProperty::Opacity(1.0), KeyframeProperty::Scale(1.0)]),
        Keyframe::new(0.5, vec![KeyframeProperty::Opacity(0.4), KeyframeProperty::Scale(1.05)]),
        Keyframe::new(1.0, vec![KeyframeProperty::Opacity(1.0), KeyframeProperty::Scale(1.0)]),
    ],
);

// Sample properties at t = 0.5s
let props = anim.sample(0.5);
assert_eq!(props[0], KeyframeProperty::Opacity(0.4));

Visual Effects (`effects`)

Provides modern compositing operations:

FilterOp: Blur(px), Brightness(factor), Contrast(factor), Grayscale(amount).
BackdropFilter: Applies real-time GPU frosted glass blur behind surfaces.
ClipPath: Geometry mask clipping (Circle, Inset, Polygon).

Production Cloud Infrastructure Example: Infrastructure Health Indicator

The following example combines Tailwind utility compilation, dynamic calc() width resolution, and keyframe property sampling to render an animated server status monitor:

rust

use strata_style::prelude::*;

pub struct ServerStatusWidget {
    pub base_style: ComputedStyle,
    pub pulse_animation: KeyframeAnimation,
}

impl ServerStatusWidget {
    pub fn new() -> Self {
        // Resolve container style using Tailwind JIT
        let base_style = TailwindEngine::resolve_classes(
            "flex flex-col p-4 bg-neutral-900 border border-neutral-800 rounded-lg gap-3"
        );

        // Define pulse keyframes for heartbeat monitor
        let pulse_animation = KeyframeAnimation::new(
            "heartbeat",
            1.5,
            CubicBezier::ease_in_out(),
            vec![
                Keyframe::new(0.0, vec![KeyframeProperty::Opacity(1.0)]),
                Keyframe::new(0.5, vec![KeyframeProperty::Opacity(0.3)]),
                Keyframe::new(1.0, vec![KeyframeProperty::Opacity(1.0)]),
            ],
        );

        Self {
            base_style,
            pulse_animation,
        }
    }

    /// Evaluates dynamic bar width subtracting fixed 32px badge offset using calc()
    pub fn compute_memory_bar_width(&self, parent_width: f32, fill_ratio: f32) -> f32 {
        let calc_str = format!("{}% - 32px", fill_ratio * 100.0);
        let expr = parse_calc(&calc_str).unwrap_or(CalcExpr::Value(Dimension::Px(0.0)));
        let ctx = CalcContext {
            parent_size: parent_width,
            ..Default::default()
        };
        expr.eval(&ctx).max(0.0)
    }

    /// Samples live opacity for heartbeat indicator
    pub fn current_pulse_opacity(&self, elapsed_seconds: f32) -> f32 {
        let props = self.pulse_animation.sample(elapsed_seconds);
        props.first().map(|p| p.value()).unwrap_or(1.0)
    }
}

Crate strata_style: CSS Engine, Cascade Solver & Tailwind JIT ​

Architectural Systems ​

CSS Lexer & Stylesheet Parser (parser) ​

Parsing Pipeline ​

Specificity & Cascade Solver (specificity, cascade) ​

The Specificity 4-Tuple ​

Cascade Resolution Algorithm (CascadeSolver::resolve) ​

Tailwind CSS v3/v4 JIT Engine (tailwind) ​

Supported Utility Categories ​

Modifier Support (resolve_classes_with_state) ​

Mathematical calc() AST Engine (calc) ​

Expression AST Representation ​

Contextual Resolution (CalcContext) ​

Declarative Keyframe Animations (keyframes) ​

Newton-Raphson Cubic-Bezier Solver ​

Animation Sampling ​

Visual Effects (effects) ​

Production Cloud Infrastructure Example: Infrastructure Health Indicator ​

Crate `strata_style`: CSS Engine, Cascade Solver & Tailwind JIT

Architectural Systems

CSS Lexer & Stylesheet Parser (`parser`)

Parsing Pipeline

Specificity & Cascade Solver (`specificity`, `cascade`)

The Specificity 4-Tuple

Cascade Resolution Algorithm (`CascadeSolver::resolve`)

Tailwind CSS v3/v4 JIT Engine (`tailwind`)

Supported Utility Categories

Modifier Support (`resolve_classes_with_state`)

Mathematical `calc()` AST Engine (`calc`)

Expression AST Representation

Contextual Resolution (`CalcContext`)

Declarative Keyframe Animations (`keyframes`)

Newton-Raphson Cubic-Bezier Solver

Animation Sampling

Visual Effects (`effects`)

Production Cloud Infrastructure Example: Infrastructure Health Indicator