feat: Add background to header

Signed-off-by: Felicitas Pojtinger <felicitas@pojtinger.com>

Author: pojntfx

data/resources.yaml

@@ -141,7 +141,7 @@ design:
     - name: logo
       description: "VanLUG logo (icon + wordmark for cards)"
     - name: header
-      description: "Banner header for Luma and OpenGraph"
+      description: "Banner header for Luma, OpenGraph and the home page background"
       photo:
         credit: "Lee Robinson"
         url: https://unsplash.com/photos/Yc9h5SJdEzI

layouts/_partials/section-home.html

@@ -2,9 +2,7 @@
   <section
     class="pf-v6-c-page__main-section pf-m-limit-width pf-m-align-center"
     style="
-      --pf-v6-c-page__main-section--BackgroundColor: var(
-        --pf-t--global--background--color--secondary--default
-      );
+      background: linear-gradient(color-mix(in srgb, var(--pf-t--global--background--color--primary--default) 80%, transparent) 0%, var(--pf-t--global--background--color--primary--default) 100%), url('{{ "design/lee-robinson-Yc9h5SJdEzI-unsplash.jpg" | relURL }}') center / cover;
       padding-block: var(--pf-t--global--spacer--3xl);
     "
   >