Settings WebUI: Add padding to cards for smaller screens

Bug: 962381, 962386
Change-Id: Ide420cf85b90b11e1b255db279f703a570fec9f3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1609670Reviewed-by: Esmael El-Moslimany <aee@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659270}

chrome/browser/resources/settings/settings_ui/settings_ui.html

@@ -102,6 +102,9 @@
 
         #main {
           min-width: auto;
+          /* Add some padding to make room for borders and to prevent focus
+           * indicators from being cropped. */
+          padding: 0 3px;
         }
       }
     </style>