CSS value parsing: lengths, colors, keywords #40

Description#

Implement CSS value parsing in the css crate to convert raw token lists into typed property values.

Acceptance Criteria#

• Parse CSS length values:
  • Absolute units: px, pt, cm, mm, in, pc
  • Font-relative units: em, rem
  • Viewport units: vw, vh, vmin, vmax (store for later resolution)
  • Percentages: 50%
  • 0 (unitless zero)
• Parse CSS color values:
  • Named colors: at least the 16 basic CSS colors + transparent
  • Hex colors: #rgb, #rrggbb, #rgba, #rrggbbaa
  • rgb() and rgba() functional notation
  • currentColor keyword
• Parse CSS keyword values:
  • inherit, initial, unset
  • Display: block, inline, inline-block, none, flex
  • Position: static, relative, absolute, fixed
  • Text: left, center, right, justify
  • Font-weight: normal, bold, numeric (100-900)
  • Font-style: normal, italic
  • Overflow: visible, hidden, scroll, auto
  • auto keyword for margins/width/height
• Represent parsed values as a CssValue enum with typed variants
• Parse shorthand properties into longhand (at least margin, padding, border, background)
• Write comprehensive tests

Dependencies#

• CSS tokenizer

Implementation Notes#

• This provides the typed value layer between raw tokens and computed styles
• Shorthand expansion is critical for the cascade to work correctly