fix: markup headings and bold text visible in light mode

src/lib/markup.tsx

@@ -16,7 +16,7 @@ function parseInline(text: string, keyPrefix: string): React.ReactNode[] {
       parts.push(text.slice(lastIndex, match.index));
     }
     if (match[2]) {
-      parts.push(<strong key={`${keyPrefix}-b${key++}`} className="font-semibold text-white">{match[2]}</strong>);
+      parts.push(<strong key={`${keyPrefix}-b${key++}`} className="font-semibold text-neutral-900 dark:text-white">{match[2]}</strong>);
     } else if (match[3]) {
       parts.push(<em key={`${keyPrefix}-i${key++}`}>{match[3]}</em>);
     }
@@ -47,7 +47,7 @@ export function formatMarkup(text: string): React.ReactNode {
     // ## Heading
     if (trimmed.startsWith("## ")) {
       elements.push(
-        <span key={key++} className="block mt-3 mb-1 text-sm font-semibold text-white">
+        <span key={key++} className="block mt-3 mb-1 text-sm font-semibold text-neutral-900 dark:text-white">
           {parseInline(trimmed.slice(3), `h${key}`)}
         </span>
       );