message: Make the empty thread panel fill BaseCard
  Use border-box to make maintaining the layout more intuitive.
diff: @@ -316,6 +316,8 @@ limitations under the License.
  bottom: 0;
  left: 0;
  padding: 20px;
  + box-sizing: border-box; // Include padding and border
  + width: 100%;
  h2 {
  color: $primary-content;
  