Tabs: add focus style (#9441)

packages/tabs/src/tab-nav.vue

@@ -146,6 +146,7 @@
         }
         tabList[nextIndex].focus(); // 改变焦点元素
         tabList[nextIndex].click(); // 选中下一个tab
+        this.setFocus();
       },
       setFocus() {
         this.isFocus = true;

packages/theme-chalk/src/tabs.scss

@@ -99,6 +99,11 @@
       outline: none;
     }
 
+    &:focus.is-active.is-focus:not(:active) {
+      box-shadow: 0 0 2px 2px #409eff inset;
+      border-radius: 3px;
+    }
+
     & .el-icon-close {
       border-radius: 50%;
       text-align: center;