Fix dark highlighting themes missing base text color

Two issues prevented dark syntax highlighting themes (zenburn,
espresso, etc.) from setting a base text color when paired with
a light theme:

1. In format-html-scss.ts, the $code-block-color SCSS variable
   extraction was gated by !isAdaptive. When users specify separate
   light/dark themes ({light: kate, dark: zenburn}), isAdaptive
   returns true (because both keys exist), so $code-block-color
   was never emitted. Move the text-color extraction outside the
   isAdaptive guard — adaptive themes handle their own background,
   but text-color still needs to propagate.

2. In _bootstrap-rules.scss, $code-block-color was only applied to
   container elements (div.sourceCode, pre.sourceCode), but the
   light theme's syntax highlighting CSS generates span-level rules
   (code.sourceCode > span { color: #1f1c1b }) that override
   container inheritance. Add matching span-level selectors.

Fixes #14099

Author: jdonaldson

src/format/html/format-html-scss.ts

@@ -314,7 +314,13 @@ export function resolveTextHighlightingLayer(
           true,
         );
       }
+    }
 
+    // Inject a text color regardless of adaptive status. Adaptive themes
+    // handle their own bg, but when separate light/dark themes are paired
+    // (e.g. kate + zenburn), the dark theme still needs its text-color
+    // emitted as $code-block-color so Bootstrap rules can apply it.
+    if (themeDescriptor) {
       const textColor = themeDescriptor.json["text-color"] as string;
       if (textColor) {
         layer.defaults = layer.defaults + "\n" + outputVariable(

src/resources/formats/html/bootstrap/_bootstrap-rules.scss

@@ -863,6 +863,14 @@ div.sourceCode {
   div.sourceCode pre.sourceCode {
     color: $code-block-color;
   }
+  // Themes that omit "Normal" from text-styles (e.g. zenburn, espresso)
+  // don't generate a span-level color rule in the syntax highlighting CSS.
+  // When layered with a light theme that does, the light theme's near-black
+  // span color persists in dark mode. This ensures a base span color is set.
+  pre > code.sourceCode > span,
+  code.sourceCode > span {
+    color: $code-block-color;
+  }
 }
 
 pre.sourceCode {