Use color-mix for clearly distinct background tones

- Body: var(--b1) (baseline)
- Cards: color-mix(var(--b1) + 8% white) = lighter surface
- Navbar: color-mix(var(--b1) + 20% black) = darker header
- Cards hover: same as navbar
- Search dropdown: matches navbar darkness

src/main/resources/templates/fragments/feed-entries.html

@@ -1,5 +1,5 @@
 {#if entries.isEmpty()}
-<div style="background:var(--b2);border:1px solid var(--b3);border-radius:0.5rem;padding:3rem;text-align:center">
+<div style="background:color-mix(in srgb,var(--b1),white 8%);border:1px solid var(--b3);border-radius:0.5rem;padding:3rem;text-align:center">
   <p style="font-size:1.125rem;color:var(--bc);opacity:0.6">No releases found</p>
   <p style="font-size:0.875rem;color:var(--bc);opacity:0.4;margin-top:0.5rem">Add artists to your collection to see their releases here</p>
 </div>
@@ -7,9 +7,9 @@
 <div style="display:flex;flex-direction:column;gap:1.5rem">
   {#for entry in entries}
   <a href="https://musicbrainz.org/release-group/{entry.mbid}" target="_blank" rel="noopener noreferrer"
-     style="display:flex;text-decoration:none;background:var(--b2);border:1px solid var(--b3);border-radius:0.5rem;overflow:hidden;transition:background 0.15s"
-     onmouseover="this.style.background='var(--b3)'"
-     onmouseout="this.style.background='var(--b2)'">
+     style="display:flex;text-decoration:none;background:color-mix(in srgb,var(--b1),white 8%);border:1px solid var(--b3);border-radius:0.5rem;overflow:hidden;transition:background 0.15s"
+     onmouseover="this.style.background='color-mix(in srgb,var(--b1),black 20%)'"
+     onmouseout="this.style.background='color-mix(in srgb,var(--b1),white 8%)'">
     <div style="width:250px;height:250px;flex-shrink:0;overflow:hidden;background:var(--b3)">
       <img src="https://coverartarchive.org/release-group/{entry.mbid}/front-250"
            alt="{entry.title}" style="width:100%;height:100%;object-fit:cover;display:block"