fix(theme): improve Chinese font handling

close #2036

Author: yyx990803

src/client/theme-default/styles/base.css

@@ -26,7 +26,7 @@ body {
   color: var(--vp-c-text-1);
   background-color: var(--vp-c-bg);
   direction: ltr;
-  font-synthesis: none;
+  font-synthesis: style;
   text-rendering: optimizeLegibility;
   -webkit-font-smoothing: antialiased;
   -moz-osx-font-smoothing: grayscale;

src/client/theme-default/styles/fonts.css

@@ -155,3 +155,11 @@ html body {
   unicode-range: U+0102-0103, U+0110-0111, U+0128-0129, U+0168-0169, U+01A0-01A1,
     U+01AF-01B0, U+1EA0-1EF9, U+20AB;
 }
+
+/* Chinese quotes rendering fix. 中英文弯引号共享 Unicode 码位，确保引号使用中文字体渲染 */
+@font-face {
+  font-family: 'Chinese Quotes';
+  src: local('PingFang SC Regular'), local('PingFang SC'), local('SimHei'),
+    local('Source Han Sans SC');
+  unicode-range: U+2018, U+2019, U+201C, U+201D; /* 分别是 ‘’“” */
+}

src/client/theme-default/styles/vars.css

@@ -143,10 +143,10 @@
  * -------------------------------------------------------------------------- */
 
 :root {
-  --vp-font-family-base: 'Inter var', 'Inter', ui-sans-serif, system-ui,
-    -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue',
-    Helvetica, Arial, 'Noto Sans', sans-serif, 'Apple Color Emoji',
-    'Segoe UI Emoji', 'Segoe UI Symbol', 'Noto Color Emoji';
+  --vp-font-family-base: 'Chinese Quotes', 'Inter var', 'Inter', ui-sans-serif,
+    system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto,
+    'Helvetica Neue', Helvetica, Arial, 'Noto Sans', sans-serif,
+    'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol', 'Noto Color Emoji';
   --vp-font-family-mono: ui-monospace, SFMono-Regular, 'SF Mono', Menlo, Monaco,
     Consolas, 'Liberation Mono', 'Courier New', monospace;
 }