fix(theme): code block style is broken inside custom block (#2664)

src/client/theme-default/styles/components/vp-doc.css

@@ -226,6 +226,7 @@
 
 .vp-doc .custom-block div[class*='language-'] {
   margin: 8px 0;
+  border-radius: 8px;
 }
 
 .vp-doc .custom-block div[class*='language-'] code {
@@ -233,6 +234,11 @@
   background-color: transparent;
 }
 
+.vp-doc .custom-block .vp-code-group .tabs {
+  margin: 0;
+  border-radius: 8px 8px 0 0;
+}
+
 /**
  * Code
  * -------------------------------------------------------------------------- */