Settings[DICE]: fix sign-in button spacing

Bug: 813716
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I44ca92b701d1fc1140bdbfb577fb9cb0a5680219
Reviewed-on: https://chromium-review.googlesource.com/953972
Commit-Queue: Scott Chen <scottchen@chromium.org>
Reviewed-by: Dave Schuyler <dschuyler@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541952}

chrome/browser/resources/settings/settings_shared_css.html

@@ -90,8 +90,9 @@
         -webkit-margin-start: 16px;
       }
 
-      /* Adjust the margin between the separator and the first button. */
-      .separator + paper-button {
+      /* Adjust the margin between the separator and the first button. Exclude
+       * .action-button since it has a background thus is visually different. */
+      .separator + paper-button:not(.action-button) {
         -webkit-margin-start: calc(var(--cr-button-edge-spacing) * -1);
       }