style: change blog content h1-h4 color to #1F2937

Agent-Logs-Url: https://github.com/recodehive/recode-website/sessions/f0d85b6a-44d0-428e-9f1e-98be4e8bfc2f

Co-authored-by: sanjay-kv <30715153+sanjay-kv@users.noreply.github.com>

Author: Copilot

src/css/custom.css

@@ -2160,6 +2160,20 @@ html[data-theme="dark"] .blog-post-page .markdown {
   margin-bottom: 0.5rem !important;
 }
 
+.blog-post-page .markdown h1,
+.blog-post-page .markdown h2,
+.blog-post-page .markdown h3,
+.blog-post-page .markdown h4 {
+  color: #1F2937 !important;
+}
+
+html[data-theme="dark"] .blog-post-page .markdown h1,
+html[data-theme="dark"] .blog-post-page .markdown h2,
+html[data-theme="dark"] .blog-post-page .markdown h3,
+html[data-theme="dark"] .blog-post-page .markdown h4 {
+  color: #D1D5DB !important;
+}
+
 /* ── Large desktop (≥1400px) — wider content ── */
 @media (min-width: 1400px) {
   .blog-wrapper .container>.row>.col.col--3 {