[improvement] Tab: split less file

packages/index.less

@@ -22,6 +22,7 @@
 @import './steps/index';
 @import './step/index';
 @import './tag/index';
+@import './tab/index';
 @import './tabs/index';
 @import './tabbar/index';
 @import './tabbar-item/index';

packages/tab/index.less

@@ -0,0 +1,17 @@
+@import '../style/var';
+
+.van-tab {
+  &__pane {
+    &,
+    &-wrapper {
+      flex-shrink: 0;
+      box-sizing: border-box;
+      width: 100%;
+    }
+
+    &-wrapper--inactive {
+      height: 0;
+      overflow: visible;
+    }
+  }
+}

packages/tabs/index.less

@@ -141,17 +141,3 @@
     }
   }
 }
-
-.van-tab__pane {
-  &,
-  &-wrapper {
-    flex-shrink: 0;
-    box-sizing: border-box;
-    width: 100%;
-  }
-
-  &-wrapper--inactive {
-    height: 0;
-    overflow: visible;
-  }
-}