website: Change the color for headers to match the old ones

Change-Id: Ic4112d5daaf4d96f551af2fbfb5222966df41e62
diff --git a/stylesheets/constants.less b/stylesheets/constants.less
index cb2ddd5..a0cbb8b 100644
--- a/stylesheets/constants.less
+++ b/stylesheets/constants.less
@@ -7,6 +7,7 @@
 @color-blue-grey-50: #eceff1;
 @color-blue-grey-100: #cfd8dc;
 @color-blue-grey-500: #607d8b;
+@color-blue-grey-800: #37474f;
 @color-deep-orange-A200: #ff6e40;
 @color-cyan-700: #0097a7;
 @color-cyan-800: #00838f;
diff --git a/stylesheets/index.less b/stylesheets/index.less
index 8992980..08a102f 100644
--- a/stylesheets/index.less
+++ b/stylesheets/index.less
@@ -40,6 +40,7 @@
 }
 
 h1, h2, h3, h4, h5, h6 {
+  color: @color-blue-grey-800;
   margin: 1.2em 0 0.4em;
   line-height: 1.5;
 }
@@ -52,6 +53,7 @@
   line-height: 48px;
 }
 h1 {
+  color: @color-blue-grey-500;
   font-size: 34px;
   line-height: 40px;
 }
@@ -69,6 +71,7 @@
   font-size: 14px;
 }
 h6 {
+  color: @color-blue-grey-500;
   font-size: 12px;
 }