docs: correct filenames in `guide/extending-default-theme.md`

docs/en/guide/extending-default-theme.md

@@ -55,7 +55,7 @@ export default DefaultTheme
 ```
 
 ```css
-/* .vitepress/theme/custom.css */
+/* .vitepress/theme/my-fonts.css */
 :root {
   --vp-font-family-base: /* normal text font */
   --vp-font-family-mono: /* code font */

docs/es/guide/extending-default-theme.md

@@ -55,7 +55,7 @@ export default DefaultTheme
 ```
 
 ```css
-/* .vitepress/theme/custom.css */
+/* .vitepress/theme/my-fonts.css */
 :root {
   --vp-font-family-base: /* fuente de texto normal */
   --vp-font-family-mono: /* fuente de código */

docs/ko/guide/extending-default-theme.md

@@ -55,7 +55,7 @@ export default DefaultTheme
 ```
 
 ```css
-/* .vitepress/theme/custom.css */
+/* .vitepress/theme/my-fonts.css */
 :root {
   --vp-font-family-base: /* 일반 텍스트 폰트 */
   --vp-font-family-mono: /* 코드 폰트 */

docs/pt/guide/extending-default-theme.md

@@ -55,7 +55,7 @@ export default DefaultTheme
 ```
 
 ```css
-/* .vitepress/theme/custom.css */
+/* .vitepress/theme/my-fonts.css */
 :root {
   --vp-font-family-base: /* fonte de texto normal */
   --vp-font-family-mono: /* fonte de código */

docs/ru/guide/extending-default-theme.md

@@ -55,7 +55,7 @@ export default DefaultTheme
 ```
 
 ```css
-/* .vitepress/theme/custom.css */
+/* .vitepress/theme/my-fonts.css */
 :root {
   --vp-font-family-base: /* normal text font */ --vp-font-family-mono:
     /* code font */;

docs/zh/guide/extending-default-theme.md

@@ -55,7 +55,7 @@ export default DefaultTheme
 ```
 
 ```css
-/* .vitepress/theme/custom.css */
+/* .vitepress/theme/my-fonts.css */
 :root {
   --vp-font-family-base: /* normal text font */
   --vp-font-family-mono: /* code font */