fix(theme): code group tab divider not showing full-width (vuejs#2701)

Author: brc-dd

src/client/theme-default/styles/components/vp-code-group.css

@@ -11,16 +11,7 @@
   background-color: var(--vp-code-tab-bg);
   overflow-x: auto;
   overflow-y: hidden;
-}
-
-.vp-code-group .tabs::after {
-  position: absolute;
-  right: 0;
-  bottom: 0;
-  left: 0;
-  height: 1px;
-  background-color: var(--vp-code-tab-divider);
-  content: '';
+  box-shadow: inset 0 -1px var(--vp-code-tab-divider);
 }
 
 @media (min-width: 640px) {