WebUI: Remove extra margin between multiple buttons on Appearance page

Bug: 867169
Change-Id: Ib92bcc9a46653181fda1fd23ea6da63daf3b081d
Reviewed-on: https://chromium-review.googlesource.com/c/1354485
Commit-Queue: John Lee <johntlee@chromium.org>
Reviewed-by: Esmael El-Moslimany <aee@chromium.org>
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612904}

chrome/browser/resources/settings/appearance_page/appearance_page.html

@@ -22,10 +22,6 @@
 <dom-module id="settings-appearance-page">
   <template>
     <style include="settings-shared md-select iron-flex">
-      .secondary-button ~ .secondary-button {
-        margin-inline-start: 12px;
-      }
-
       /* Lines up with cr-input. */
       #custom-input {
         --cr-radio-button-disc: {