WebUI: Move --cr-section mixin to the only place it is used

Bug: 973674
Change-Id: I88427bb8259bda94af6550228e7925212df791a8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2341178Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796947}

chrome/browser/resources/settings/settings_shared_css.html

@@ -225,7 +225,11 @@
       /* A settings-box is a horizontal row of text or controls within a
        * setting section (page or subpage). */
       .settings-box {
-        @apply --cr-section;
+        align-items: center;
+        border-top: var(--cr-separator-line);
+        display: flex;
+        min-height: var(--cr-section-min-height);
+        padding: 0 var(--cr-section-padding);
       }
 
       .settings-box.no-padding {

ui/webui/resources/cr_elements/shared_vars_css.html

@@ -155,16 +155,6 @@
     --cr-section-indent-padding: calc(
         var(--cr-section-padding) + var(--cr-section-indent-width));
 
-    /* TODO(crbug.com/973674): Do not use this mixin. Use the class cr-row
-     * from shared_style_css.html instead. */
-    --cr-section: {
-      align-items: center;
-      border-top: var(--cr-separator-line);
-      display: flex;
-      min-height: var(--cr-section-min-height);
-      padding: 0 var(--cr-section-padding);
-    }
-
     --cr-section-vertical-margin: 21px;
 
     --cr-centered-card-max-width: 680px;