Fixes header styling issue introduced in SOL-734 (#8389) by reverting heights to…

Fixes header styling issue introduced in SOL-734 (#8389) by reverting heights to what they were before that PR

lms/static/sass/shared/_header.scss

@@ -8,6 +8,7 @@ header.global {
   background: $header-bg;
   position: relative;
   width: 100%;
+  height: 76px;
 
   .wrapper-header {
     @include clearfix();
@@ -30,8 +31,9 @@ header.global {
 
   nav {
     @include clearfix();
+    height: 40px;
     margin: 0 auto;
-    padding: 18px ($baseline/2) 12px;
+    padding: 18px ($baseline/2) 0;
     max-width: grid-width(12);
   }