[Media Router] Update route-details styling.

Per conversation with UX, this change:
- Removes the unused (and incorrect) background color for the media-router-container.
- Updates the margins of the non-custom controller details.
- Updates the sizing and styling of the stop casting button in the route-details view.

Final changes to styling/redlines per offline conversation after mocks came out.

BUG=567807

Review URL: https://codereview.chromium.org/1507873003

Cr-Commit-Position: refs/heads/master@{#364389}
diff --git a/chrome/browser/resources/media_router/elements/route_details/route_details.css b/chrome/browser/resources/media_router/elements/route_details/route_details.css
index 22b88fd..1b948dd 100644
--- a/chrome/browser/resources/media_router/elements/route_details/route_details.css
+++ b/chrome/browser/resources/media_router/elements/route_details/route_details.css
@@ -5,8 +5,8 @@
 #close-route-button {
   -webkit-padding-end: 24px;
   background-color: white;
-  line-height: 32px;
-  margin: 0;
+  line-height: 12px;
+  margin: 12px 0;
   text-align: end;
   width: 100%;
 }
@@ -18,10 +18,9 @@
 }
 
 #route-information {
-  -webkit-padding-start: 30px;
+  -webkit-padding-start: 44px;
   background-color: white;
   font-size: 1.2em;
-  height: 40px;
+  margin-top: 16px;
   overflow: hidden;
-  padding: 20px 30px;
 }
diff --git a/chrome/browser/resources/media_router/elements/route_details/route_details.html b/chrome/browser/resources/media_router/elements/route_details/route_details.html
index d0237e0..f1feac4 100644
--- a/chrome/browser/resources/media_router/elements/route_details/route_details.html
+++ b/chrome/browser/resources/media_router/elements/route_details/route_details.html
@@ -10,7 +10,7 @@
     <extensionview id="custom-controller"
         hidden$="[[isCustomControllerHidden_]]">
     </extensionview>
-    <paper-button raised id="close-route-button" class="button"
+    <paper-button flat id="close-route-button" class="button"
         on-click="closeRoute_">
       <span>[[stopCastingButtonText_]]</span>
     </paper-button>
diff --git a/chrome/browser/resources/media_router/media_router.css b/chrome/browser/resources/media_router/media_router.css
index e44f31b..00e539a2 100644
--- a/chrome/browser/resources/media_router/media_router.css
+++ b/chrome/browser/resources/media_router/media_router.css
@@ -9,7 +9,6 @@
 }
 
 #media-router-container {
-  background-color: rgb(246, 246, 246);
   display: flex;
   flex-direction: column;
 }