style(webui): improve typography with Apple-inspired font stack and CJK support

- Add explicit CJK fonts (PingFang SC, Noto Sans SC, Microsoft YaHei) and
  programmer fonts (JetBrains Mono, Fira Code, Cascadia Code) to Tailwind config
- Bump prose base size from prose-sm (14px) to prose-lg (18px) for sharper CJK rendering
- Unify user/assistant message font size at 18px with CJK-aware line-height (1.8)
- Replace pure black/white foreground with Apple-style warm grays (#1d1d1f / #f5f5f7)
- Override Tailwind Typography colors to use design tokens for consistency
- Add negative letter-spacing on headings for tighter, more polished look

webui/index.html

@@ -26,8 +26,10 @@
         background: #ffffff;
         color: #0a0a0a;
         font-family:
-          ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI",
+          system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
-          Roboto, "Helvetica Neue", Arial, "Noto Sans", sans-serif;
+          "Helvetica Neue", Arial, "Noto Sans", "Noto Sans SC",
+          "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei",
+          sans-serif;
       }
 
       html.dark body {

webui/src/components/MarkdownTextRenderer.tsx

@@ -24,10 +24,10 @@ export default function MarkdownTextRenderer({
   return (
     <div
       className={cn(
-        "markdown-content prose prose-sm max-w-none dark:prose-invert",
+        "markdown-content prose prose-lg max-w-none dark:prose-invert",
-        "prose-headings:mt-4 prose-headings:mb-2 prose-headings:font-semibold",
+        "prose-headings:mt-4 prose-headings:mb-2 prose-headings:font-semibold prose-headings:tracking-tight",
-        "prose-h1:text-lg prose-h2:text-base prose-h3:text-[0.95rem] prose-h4:text-sm",
+        "prose-h1:text-xl prose-h2:text-lg prose-h3:text-base prose-h4:text-sm",
-        "prose-p:my-2 prose-p:leading-relaxed",
+        "prose-p:my-2",
         "prose-ul:my-2 prose-ol:my-2 prose-li:my-0.5",
         "prose-blockquote:my-3 prose-blockquote:border-l-2 prose-blockquote:font-normal",
         "prose-blockquote:not-italic prose-blockquote:text-foreground/80",
@@ -38,6 +38,7 @@ export default function MarkdownTextRenderer({
         "prose-table:my-3 prose-th:text-left prose-th:font-medium",
         className,
       )}
+      style={{ lineHeight: "var(--cjk-line-height)" }}
     >
       <ReactMarkdown
         remarkPlugins={[remarkGfm, remarkMath]}

webui/src/components/MessageBubble.tsx

@@ -37,7 +37,7 @@ export function MessageBubble({ message }: MessageBubbleProps) {
         <p
           className={cn(
             "ml-auto w-fit rounded-[18px] border border-border/60 bg-secondary/70 px-4 py-2",
-            "text-right text-sm whitespace-pre-wrap break-words",
+            "text-right text-[18px]/[1.8] whitespace-pre-wrap break-words",
             "shadow-[0_10px_24px_-18px_rgba(0,0,0,0.55)]",
           )}
         >
@@ -49,7 +49,7 @@ export function MessageBubble({ message }: MessageBubbleProps) {
 
   const empty = message.content.trim().length === 0;
   return (
-    <div className={cn("w-full text-sm leading-relaxed", baseAnim)}>
+    <div className={cn("w-full text-sm", baseAnim)} style={{ lineHeight: "var(--cjk-line-height)" }}>
       {empty && message.isStreaming ? (
         <TypingDots />
       ) : (

webui/src/globals.css

@@ -6,12 +6,12 @@
 @layer base {
   :root {
     --background: 0 0% 100%;
-    --foreground: 0 0% 3.9%;
+    --foreground: 240 3% 12%;
     --card: 0 0% 100%;
-    --card-foreground: 0 0% 3.9%;
+    --card-foreground: 240 3% 12%;
     --popover: 0 0% 100%;
-    --popover-foreground: 0 0% 3.9%;
+    --popover-foreground: 240 3% 12%;
-    --primary: 0 0% 9%;
+    --primary: 240 4% 16%;
     --primary-foreground: 0 0% 98%;
     --secondary: 0 0% 96.1%;
     --secondary-foreground: 0 0% 9%;
@@ -34,12 +34,12 @@
 
   .dark {
     --background: 0 0% 10%;
-    --foreground: 0 0% 98%;
+    --foreground: 240 4% 96%;
     --card: 0 0% 12%;
-    --card-foreground: 0 0% 98%;
+    --card-foreground: 240 4% 96%;
     --popover: 0 0% 12%;
-    --popover-foreground: 0 0% 98%;
+    --popover-foreground: 240 4% 96%;
-    --primary: 0 0% 98%;
+    --primary: 240 5% 98%;
     --primary-foreground: 0 0% 9%;
     --secondary: 0 0% 12%;
     --secondary-foreground: 0 0% 98%;
@@ -72,11 +72,7 @@
   }
 
   body {
-    @apply bg-background text-foreground antialiased;
+    @apply bg-background text-foreground font-sans antialiased;
-    font-family:
-      ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI",
-      Roboto, "Helvetica Neue", Arial, "Noto Sans", sans-serif,
-      "Apple Color Emoji", "Segoe UI Emoji";
   }
 
   ::selection {
@@ -97,6 +93,30 @@
     @apply mb-0;
   }
 
+  /* Override Tailwind Typography's built-in colors with our design tokens
+     so assistant messages use the same --foreground as user messages. */
+  .markdown-content {
+    --tw-prose-body: hsl(var(--foreground));
+    --tw-prose-headings: hsl(var(--foreground));
+    --tw-prose-bold: hsl(var(--foreground));
+    --tw-prose-lead: hsl(var(--foreground));
+  }
+
+  /* CJK-friendly line-height: prose paragraphs default to 1.625 which is
+     tight for Chinese/Japanese/Korean characters. Bump to 1.8 for better
+     readability when the browser detects a CJK primary font. */
+  :lang(zh),
+  :lang(zh-CN),
+  :lang(zh-TW),
+  :lang(zh-HK),
+  :lang(ja),
+  :lang(ko) {
+    --cjk-line-height: 1.8;
+  }
+  :root {
+    --cjk-line-height: 1.625;
+  }
+
   /* Subtle scrollbar that doesn't fight the dark background. */
   .scrollbar-thin {
     scrollbar-width: thin;

webui/tailwind.config.js

@@ -14,6 +14,34 @@ export default {
       },
     },
     extend: {
+      fontFamily: {
+        sans: [
+          "system-ui",
+          "-apple-system",
+          "BlinkMacSystemFont",
+          '"Segoe UI"',
+          "Roboto",
+          '"Helvetica Neue"',
+          "Arial",
+          '"Noto Sans"',
+          '"Noto Sans SC"',
+          '"PingFang SC"',
+          '"Hiragino Sans GB"',
+          '"Microsoft YaHei"',
+          "sans-serif",
+          '"Apple Color Emoji"',
+          '"Segoe UI Emoji"',
+        ],
+        mono: [
+          '"JetBrains Mono"',
+          '"Fira Code"',
+          '"Cascadia Code"',
+          '"Source Code Pro"',
+          "Menlo",
+          "Consolas",
+          "monospace",
+        ],
+      },
       borderRadius: {
         lg: "var(--radius)",
         md: "calc(var(--radius) - 2px)",