Soften channel banner gradient opacity

css/tokens.css

@@ -25,6 +25,11 @@
     var(--surface-overlay-banner-base) 82%,
     transparent
   );
+  --surface-overlay-banner-bottom: color-mix(
+    in srgb,
+    var(--surface-overlay-banner-base) 75%,
+    transparent
+  );
   --surface-overlay-banner-soft: color-mix(
     in srgb,
     var(--surface-overlay-banner-base) 56%,
@@ -46,7 +51,7 @@
   );
   --surface-overlay-banner-gradient-channel: linear-gradient(
     to top,
-    var(--surface-overlay-banner-opaque) 0%,
+    var(--surface-overlay-banner-bottom) 0%,
     var(--surface-overlay-banner-strong) 12%,
     var(--surface-overlay-banner-soft) 20%,
     var(--surface-overlay-banner-faint) 26%,