Apply max width to all input elements.

Update form class with better name and add form-conrainer--narrow class.

templates/portfolios/admin.html

@@ -13,7 +13,7 @@
   <div v-cloak class="portfolio-admin">
     {% include "fragments/flash.html" %}
     <!-- max width of this section is 460px -->
-    <section class="form-container__half">
+    <section class="form-container--narrow">
       <h3>Portfolio name and component</h3>
       {% if user_can(permissions.EDIT_PORTFOLIO_NAME) %}
         <base-form inline-template>