fix: make table captions and figure captions visible in light mode (#535)

The pydata-sphinx-theme styles table caption and figure figcaption with
--pst-color-text-muted, which the SCORE theme sets to #FFF for the dark
header background. This made captions invisible on the light page body.

Add targeted overrides for these content-area elements in light mode
instead of changing the shared CSS variable, which would break the
header/nav styling.

Fixes #529

Author: AlexanderLanin

src/extensions/score_layout/assets/css/score.css

@@ -143,6 +143,13 @@ blockquote {
     color: var(--pst-color-text-base);
 }
 
+/* Override text-muted for content-area elements that need readable text on light backgrounds.
+   --pst-color-text-muted is set to #FFF for the dark header, but these sit on the page body. */
+html[data-theme="light"] table caption,
+html[data-theme="light"] figure figcaption {
+    color: var(--pst-color-text-base);
+}
+
 .admonition, div.admonition {
     background-color: rgba(0,0,0,0.1);
 }