Fix issue left by commit 061fe0a: delete margin (#536)

Since commit 061fe0a replaced the margin with gap in solution.css, the margin should be deleted in style.css as well.

Author: zhangsherry

flex/06-flex-layout/style.css

@@ -23,5 +23,4 @@ input {
   border-radius: 16px;
   padding: 8px 24px;
   width: 400px;
-  margin-bottom: 16px;
 }