Fix dark-mode white bar (html bg + body min-height) and centred container

- html now gets --color-bg (not just body) + body min-height:100vh, so a short
  page never reveals a light html canvas as a bar at the bottom.
- Bulma adapter: force dark html/body + transparent sections, and centre
  .container.fullwidth with !important (beats Bulma's .is-marginless margin:0).

adapters/bulma.css

@@ -102,10 +102,20 @@ hr { background-color: var(--color-border); }
 details summary { color: var(--color-accent); }
 .section { padding-top: 2rem; }
 
+/* Kill any light Bulma canvas (html/body/section) so dark mode is fully dark. */
+html, body { background-color: var(--color-bg) !important; }
+body { min-height: 100vh; }
+.content.has-navbar-fixed-top, #pageContent, .section, .hero, .hero-body, .footer { background-color: transparent !important; }
+
 /* Responsive content width: full-bleed on phones, a centred readable column on
    large screens (so a wishlist doesn't stretch edge-to-edge on a desktop). The
-   app marks a wrapper with .container.fullwidth; constrain it past tablet. */
+   app marks a wrapper with .container.fullwidth; centre + constrain past tablet.
+   !important is needed to beat Bulma's .is-marginless (margin:0 !important). */
 @media (min-width: 769px) {
-  .container.fullwidth { max-width: 52rem; margin-left: auto; margin-right: auto; }
+  .container.fullwidth {
+    max-width: 52rem;
+    margin-left: auto !important;
+    margin-right: auto !important;
+  }
   .container.fullwidth.is-wide { max-width: 72rem; }
 }

weirsoe-theme.css

@@ -70,8 +70,11 @@
 }
 
 /* ---------- base ---------- */
-html { scroll-behavior: smooth; }
+/* html AND body get the bg (and body fills the viewport) so a short page never
+   reveals a light html canvas as a bar at the bottom. */
+html { scroll-behavior: smooth; background-color: var(--color-bg); }
 body {
+  min-height: 100vh;
   background-color: var(--color-bg);
   color: var(--color-text);
   font-family: var(--wt-font-sans);