Remove the gap above docs pages left from the old site banner (#75485)

custom.css still padded the docs layout by 163px and offset anchor
targets by 161px, sized for a 40px banner above a 121px navbar. The site
now has no banner, a 90px navbar (80px at 1280px and below), and the
theme already pads the body for the navbar, so docs content started
253px down instead of 130px.

Drop the padding override so the theme's 40px applies, and size the
anchor offset to the navbar plus the same 40px.

devel-common/sphinx_design/static/custom.css

@@ -44,10 +44,6 @@ div.admonition.warning {
 /* Patches as of moving to Sphinx 7 to get layout to previous state  */
 /* Needs to be cleaned in a follow-up to source this from the origin style in */
 /* https://github.com/apache/airflow-site/blob/main/landing-pages/site/assets/scss/_rst-content.scss */
-.base-layout {
-  padding-top: 163px !important; /* banner + navbar + 2px padding */
-}
-
 section {
   padding-top: 0rem !important;
   padding-bottom: 0rem !important;
@@ -87,14 +83,14 @@ a.headerlink svg {
 :target::before {
   content: "";
   display: block;
-  height: 161px; /* 40px banner + 121px navbar */
-  margin: -161px 0 0; /* negative fixed header height */
+  height: 130px; /* 90px navbar + 40px gap */
+  margin: -130px 0 0; /* negative of the height above */
 }
 
 @media (max-width: 1280px) {
   :target::before {
-    height: 117px; /* 40px banner + 77px mobile navbar */
-    margin: -117px 0 0; /* negative fixed header height */
+    height: 120px; /* 80px mobile navbar + 40px gap */
+    margin: -120px 0 0; /* negative of the height above */
   }
 }