[MD settings] icon color and sizing centralized

chrome/browser/resources/settings/settings_shared_css.html

 <!-- Common styles for Material Design settings. -->
 <dom-module id="settings-shared">
   <template>
     <style>
       :root {
         --checkbox-margin-start: 2px;
         --checkbox-size: 16px;
         --checkbox-spacing: 18px;
+        --iron-icon-fill-color: var(--paper-grey-500);
+        --iron-icon-height: 20px;
+        --iron-icon-stroke-color: var(--paper-grey-500);
+        --iron-icon-width: 20px;
+        --paper-icon-button: {
+          width: 36px;
+          height: 36px;
+        }
+        --settings-background-color: var(--paper-blue-grey-50);
         --settings-secondary: {
           color: var(--paper-grey-500);
           font-weight: 400;
         }
+        --settings-side-nav-color: var(--google-grey-600);
+        /* TODO(dschuyler): replace this rgb with a --paper color */
+        --settings-title-bar-color: rgb(52, 73, 94);
       }
 
       h2 {
         @apply(--layout-center);
         color: var(--paper-grey-500);
         display: flex;
         font-size: 100%;
         font-weight: 500;
         margin: 0;
         min-height: 40px;
       }
 
-      iron-icon {
-        color: var(--paper-grey-300);
-      }
-
+      iron-icon[icon=check],
       iron-icon[icon=done] {
-        color: var(--google-green-500);
+       --iron-icon-fill-color: var(--google-green-500);
+       --iron-icon-stroke-color: var(--google-green-500);
       }
 
       paper-button {
         margin: 0;
         min-width: auto;
       }
 
       paper-button[toggles][active] {
         background-color: var(--paper-grey-300);
       }
@@ skipping 90 matching lines @@
         @apply(--layout-center);
         display: flex;
         min-height: 40px;
         padding: 0;
       }
 
       .list-item.underbar {
         border-bottom: 1px solid var(--paper-grey-300);
       }
 
-      .list-item iron-icon {
-        @apply(--layout-center);
-        height: 20px;
-        width: 20px;
-      }
-
       .list-item select {
         -webkit-margin-start: 4px;
       }
 
       .list-item > .middle {
         flex: 1;
         margin: 8px 12px;
         overflow: hidden;
         white-space: nowrap;
       }
@@ skipping 28 matching lines @@
       }
 
       .settings-box.block {
         display: block;
       }
 
       .settings-box.two-line {
         min-height: 52px;
       }
 
-      .settings-box iron-icon {
-        @apply(--layout-center);
-        height: 20px;
-        width: 20px;
-      }
-
       .settings-box .secondary {
         @apply(--settings-secondary);
       }
 
       .settings-box .middle {
         -webkit-margin-start: 16px;
         align-items: center;
         flex: auto;
       }
 
@@ skipping 32 matching lines @@
 
       .settings-checkbox-spacer {
         -webkit-margin-start: calc(
             var(--checkbox-margin-start) +
             var(--checkbox-size) +
             var(--checkbox-spacing));
       }
     </style>
   </template>
 </dom-module>