docs site: gentler header -- a pale wash instead of a saturated green bar

The light scheme filled the header and tabs with green-deep, which read as heavy. They now
use the homepage's "open source" pill colour #e8f5e8 with ink text, and the deeper greens
are kept for accents -- links, active navigation and rules -- rather than as background
fills. The dark scheme is unchanged.

publishing/brand.css

@@ -45,6 +45,11 @@
 
 /* ---------- Material for MkDocs: map the palette onto the theme ---------- */
 
+/* Light scheme: the header is a pale green WASH with dark text, not a saturated green
+ * bar. The colour is the homepage's "open source" pill (#e8f5e8). The deep greens stay
+ * for ACCENTS -- links, active navigation, rules -- rather than as large background fills.
+ */
+
 :root,
 [data-md-color-scheme="default"] {
   --md-default-bg-color: var(--cream);
@@ -53,10 +58,10 @@
   --md-default-fg-color--lighter: var(--light-muted);
   --md-default-fg-color--lightest: var(--border);
 
-  --md-primary-fg-color: var(--green-deep);
-  --md-primary-fg-color--light: var(--green-mid);
+  --md-primary-fg-color: #e8f5e8;
+  --md-primary-fg-color--light: #eef4ea;
   --md-primary-fg-color--dark: var(--green-deep);
-  --md-primary-bg-color: var(--cream);
+  --md-primary-bg-color: var(--ink);
   --md-primary-bg-color--light: rgba(250, 248, 245, 0.7);
 
   --md-accent-fg-color: var(--earth-red);