Add elevation shadow to code blocks

Give fenced code blocks a soft drop shadow (scheme-aware via --nd-code-shadow;
stronger on the dark palette where the page background is close to the block
background) so they read as elevated panels and "pop" off the page. Inner
children of wrapped blocks reset the shadow to avoid it bleeding inside the panel.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Netdocs

src/Netdocs.Theme.Material/assets/netdocs.css

@@ -159,16 +159,24 @@ body {
 
 /* Give fenced code blocks a background that reads as a distinct panel against the page
    (Material's default is only a few percent lighter, so blocks blend into the page on
-   the dark scheme). A hairline border reinforces the separation in both schemes. */
+   the dark scheme). A hairline border plus a soft drop shadow lift the block off the
+   page so it "pops" as an elevated panel in both schemes. */
+:root {
+  /* Elevation shadow for code panels — tuned per scheme below. */
+  --nd-code-shadow: 0 0.1rem 0.4rem rgba(0, 0, 0, 0.12), 0 0.05rem 0.1rem rgba(0, 0, 0, 0.08);
+}
 [data-md-color-scheme="slate"] {
   --md-code-bg-color: hsla(var(--md-hue), 15%, 22%, 1);
+  /* Darker, larger shadow so the panel clearly lifts off the dark page. */
+  --nd-code-shadow: 0 0.25rem 0.85rem rgba(0, 0, 0, 0.55), 0 0.1rem 0.25rem rgba(0, 0, 0, 0.4);
 }
 
 .md-typeset .highlight,
 .md-typeset .highlighttable {
   border: 0.05rem solid var(--md-default-fg-color--lightest);
   border-radius: 0.2rem;
   overflow: hidden;
+  box-shadow: var(--nd-code-shadow);
 }
 
 /* Bare <pre><code> blocks (not wrapped in a .highlight container) still need a
@@ -177,13 +185,17 @@ body {
 .md-typeset pre > code {
   border: 0.05rem solid var(--md-default-fg-color--lightest);
   border-radius: 0.2rem;
+  box-shadow: var(--nd-code-shadow);
 }
 
+/* Inner children of a wrapped block share the container's border/shadow, so
+   reset theirs to avoid a doubled outline or a shadow bleeding inside the panel. */
 .md-typeset .highlight pre > code,
 .md-typeset .highlighttable pre > code,
 .md-typeset .highlighttable .highlight {
   border: none;
   border-radius: 0;
+  box-shadow: none;
 }
 
 /* Blog post sidebar (`.nd-post-sidebar`) rendered in the left column on post pages: a