Diagnostics: Update overview section to be closer to mocks

- Will be updated to final mocks in the future.

Screenshots:
- Diagnostics App (before) http://shortn/_yLwB4ZAKfO
- Diagnostics App (after) http://shortn/_bUefLJUyg6

Bug: 1125150
Test: browser_tests --gtest_filter=DiagnosticsApp*
Change-Id: I8e5d1cca983b2311483a423f89ef305a53450252
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2441011
Commit-Queue: Michael Checo <michaelcheco@google.com>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812735}

chromeos/components/diagnostics_ui/resources/diagnostics_fonts_css.html

@@ -8,11 +8,13 @@
       --diagnostics-header-font-size: 22px;
       --diagnostics-data-point-title-font-size: 12px;
       --diagnostics-data-point-subtitle-font-size: 15px;
+      --diagnostics-overview-font-size: 13px;
 
       --diagnostics-default-font-weight: 500;
       --diagnostics-header-font-weight: 600;
       --diagnostics-data-point-title-font-weight: 500;
       --diagnostics-data-point-subtitle-font-weight: 550;
+      --diagnostics-overview-font-weight: 565;
 
       --diagnostics-default-text-color: var(--google-grey-900);
       --diagnostics-header-text-color: var(--google-grey-900);
@@ -38,6 +40,11 @@
           font-size: var(--diagnostics-data-point-subtitle-font-size);
           font-weight: var(--diagnostics-data-point-subtitle-font-weight);
       };
+      --diagnostics-overview-font: {
+          font-family: var(--diagnostics-default-font-family);
+          font-size: var(--diagnostics-overview-font-size);
+          font-weight: var(--diagnostics-overview-font-weight);
+      };
     }
   </style>
 </template>
\ No newline at end of file

chromeos/components/diagnostics_ui/resources/overview_card.html

 <style include="diagnostics-shared diagnostics-fonts">
   #overviewCardContainer {
-    color: var(--diagnostics-overview-text-color);
     display: flex;
   }
 
   #overviewCardContainer > div {
+    @apply --diagnostics-overview-font;
+    background-color: var(--google-grey-100);
+    border-radius: 16px;
+    color: var(--diagnostics-overview-text-color);
     margin-right: 15px;
+    padding: 10px;
   }
 
   #version {