fix russian missing

Author: hmthanh

next.config.mjs

@@ -70,7 +70,21 @@ const withMDX = nextMDX({
 
       [rehypeParseCodeMeta, { defaultShowCopyCode: true }],
       rehypeStringify,
-      rehypeKatex,
+      [
+        rehypeKatex,
+        {
+          strict: false,
+          trust: true,
+          throwOnError: false,
+          errorColor: '#cc0000',
+          macros: {
+            "\\RR": "\\mathbb{R}",
+            "\\NN": "\\mathbb{N}",
+          },
+          // Allow Unicode text in math mode
+          unicodeTextInMathMode: true,
+        },
+      ],
       [
         rehypeShiki,
         {

styles/math/mathstyles.css

@@ -12,6 +12,75 @@
   text-rendering: auto;
 }
 
+/* Fallback for Cyrillic and other Unicode characters in math mode */
+.katex .mord,
+.katex .mrel,
+.katex .mop,
+.katex .mbin,
+.katex .mopen,
+.katex .mclose,
+.katex .mpunct,
+.katex .minner {
+  font-family: 
+    KaTeX_Main,
+    SurveyWithCode,
+    "Cambria Math",
+    "STIX Two Math",
+    Times New Roman,
+    serif !important;
+}
+
+/* Additional Unicode support for Cyrillic and other non-Latin characters */
+.katex .mord.mathnormal,
+.katex .mord.mathdefault,
+.katex .mord.textord {
+  font-family: 
+    KaTeX_Main,
+    SurveyWithCode,
+    "Cambria Math",
+    "STIX Two Math",
+    Times New Roman,
+    serif !important;
+}
+
+/* Ensure Cyrillic characters use fallback fonts */
+.katex .mord[mathvariant="normal"] {
+  font-family: 
+    SurveyWithCode,
+    "Cambria Math", 
+    "STIX Two Math",
+    Times New Roman,
+    serif !important;
+  font-style: normal;
+}
+
+/* Handle Unicode text characters specifically */
+.katex .mord.mtight,
+.katex .mord.sizing,
+.katex .mord.fontsize-ensurer {
+  font-family: 
+    SurveyWithCode,
+    "Cambria Math", 
+    "STIX Two Math",
+    Times New Roman,
+    serif !important;
+}
+
+/* Force text mode elements to use regular fonts */
+.katex .text,
+.katex .textit,
+.katex .textrm,
+.katex .textsf,
+.katex .texttt,
+.katex .textbf {
+  font-family: 
+    SurveyWithCode,
+    "Cambria Math", 
+    "STIX Two Math",
+    Times New Roman,
+    serif !important;
+}
+
 .katex * {
   -ms-high-contrast-adjust: none !important;
   border-color: currentColor;