This is a very bulky way of doing this, and doesn't seem sustainable to
implement every shorthand property this way, but it's a place to start.
The "margin" CSS property now expands into its four longhands as far as
my understanding of the specs.
Note that shorthand expansion happens when we *resolve* style, not when
we parse CSS. I'm not sure this is correct anymore, I think other UA's
may actually expand shorthands into the declaration directly at parse
these days. If so, we should do this at parsing as well.
In order for this to work nicely, I made the line box classes use float
instead of int for its geometry information.
Justification works by distributing all of the whitespace on the line
(including the trailing whitespace before the line break) evenly across
the spaces in-between words.
We should probably use floating point (or maybe fixed point?) for all
the layout metrics stuff. But one thing at a time. :^)
It's now possible to set a page background image via <body background>.
Also, HtmlView now officially handles rendering the body element's
background (color, image or both.) LayoutBox is responsible for all
other background rendering.
Note that it's not yet possible to use CSS background-image properties
directly, since we can't parse them yet. :^)
Instead of using string everywhere, have the CSS parser produce enum
values, since they are a lot nicer to work with.
In the future we should generate most of this code based on a list of
supported CSS properties.
The default style for "a" tags now has { color: -libhtml-link; }.
We implement this vendor-specific property by querying the containing
document for the appropriate link color.
Currently we only use the basic link color, but in the future this can
be extended to remember visited links, etc.
Also remove the color values from the ComputedStyle object and get them
via StyleProperties instead.
At the moment, we only handle colors that Color::from_string() parses.
This was a workaround to be able to build on case-insensitive file
systems where it might get confused about <string.h> vs <String.h>.
Let's just not support building that way, so String.h can have an
objectively nicer name. :^)
