feat: Parse light-dark() CSS function by extracting the first argument and add tests.

[tacshi]

Closes #900

Added support for the CSS light-dark() function to handle SVGs exported from Draw.io with dark mode support. Previously, usvg failed to parse light-dark() and fell back to black, making text invisible on dark backgrounds.

Already tested in Zed

[tacshi]

@Its-Just-Nans Can you review this PR? I came here to fix a bug from Zed. Thanks.

[Its-Just-Nans]

@Its-Just-Nans Can you review this PR? I came here to fix a bug from Zed. Thanks.

Hi,

Maybe you should add an option to usvg::Options for the current theme and choose the light-dark value based on the option?

Note that I'm not a maintainer of resvg, only a contributor so, this is just a suggestion, but maybe not the best idea

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Edit: there is the color-scheme css props that can be in usvg Options

[tacshi]

@Its-Just-Nans Can you review this PR? I came here to fix a bug from Zed. Thanks.

Hi,

Maybe you should add an option to usvg::Options for the current theme and choose the light-dark value based on the option?

Note that I'm not a maintainer of resvg, only a contributor so, this is just a suggestion, but maybe not the best idea

Edit: there is the color-scheme css props that can be in usvg Options

Suggestion applied.

[RazrFalcon]

In general, a low-level attribute parsing is done at the svgtypes level. It also has necessary parsing utilities to simplify resolve_light_dark implementation.

Yes, it's technically not a "SVG type", but that's how resvg is "layered".

But if it is too much work, you can just add // TODO: move to svgtypes before resolve_light_dark.

[tacshi]

In general, a low-level attribute parsing is done at the svgtypes level. It also has necessary parsing utilities to simplify resolve_light_dark implementation.

Yes, it's technically not a "SVG type", but that's how resvg is "layered".

But if it is too much work, you can just add // TODO: move to svgtypes before resolve_light_dark.

Submitted: linebender/svgtypes#59