完善阅读器主题与批注界面

Sources/RDEpubReaderView/EPUBTextRendering/Typesetter/RDEPUBStyleSheetComposer.swift

@@ -136,6 +136,9 @@ struct RDEPUBStyleSheetComposer {
     private static func darkCSS(style: RDEPUBTextRenderStyle) -> String {
         let background = style.backgroundColor?.rd_cssString ?? "rgba(0, 0, 0, 1.000)"
         let text = style.textColor?.rd_cssString ?? "rgba(255, 255, 255, 1.000)"
+        // Keep the established dark-theme compatibility rules, but explicitly
+        // clear the universal background that they would otherwise apply to image
+        // attachments when converted into attributed strings by DTCoreText.
         return RDEPUBAssetRepository.string(for: .wxReadDarkCSS) + "\n\n" + """
         html, body {
           background: \(background) !important;
@@ -144,6 +147,9 @@ struct RDEPUBStyleSheetComposer {
         a {
           color: \(text) !important;
         }
+        img, video {
+          background-color: transparent !important;
+        }
         """
     }