adjust layout

src/client/styles/scss/_login.scss

@@ -278,16 +278,9 @@
 
 .login-page {
   // layout
-  .main .row {
-    @media (min-width: 350px) {
-      .col-sm-offset-4 {
-        margin-left: calc(50% - 160px);
-      }
-
-      .col-sm-4 {
-        width: 320px;
-      }
-    }
+  .main .row .login-header,
+  .login-dialog {
+    width: 320px;
   }
 
   .link-growi-org {