Improve styling.

dist/dev.greyson.playpen.svg

@@ -3,16 +3,23 @@
   Playpen app icon: a terminal pane with the vertical tab strip down its left
   edge. Shapes are kept large and high-contrast so the sidebar is still
   readable when the icon is scaled down to 32px in a launcher.
+
+  Colours track the app's dark palette — the navy surfaces of
+  `palette-dark.css` and Signal's ultramarine as the accent. An icon is the
+  one part of the app that is looked at next to a row of other icons rather
+  than on its own, so it stays on the dark scheme in both: a launcher shelf
+  where one icon repaints itself with the desktop theme is a worse result than
+  one that is simply recognisable.
 -->
 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 128 128" width="128" height="128">
   <defs>
     <linearGradient id="pane" x1="0" y1="0" x2="0" y2="1">
-      <stop offset="0" stop-color="#241f31"/>
-      <stop offset="1" stop-color="#14111b"/>
+      <stop offset="0" stop-color="#182740"/>
+      <stop offset="1" stop-color="#0b1320"/>
     </linearGradient>
     <linearGradient id="accent" x1="0" y1="0" x2="1" y2="1">
-      <stop offset="0" stop-color="#c7b3ff"/>
-      <stop offset="1" stop-color="#9b7ff0"/>
+      <stop offset="0" stop-color="#6191f3"/>
+      <stop offset="1" stop-color="#2c6bed"/>
     </linearGradient>
     <!-- Everything is clipped to the rounded body so the sidebar picks up
          the same corner radius without repeating the path. -->
@@ -24,18 +31,18 @@
   <rect x="8" y="12" width="112" height="104" rx="24" fill="url(#pane)"/>
 
   <g clip-path="url(#body)">
-    <rect x="8" y="12" width="42" height="104" fill="#2f2743"/>
-    <rect x="49" y="12" width="2" height="104" fill="#3d3357"/>
+    <rect x="8" y="12" width="42" height="104" fill="#1c2c45"/>
+    <rect x="49" y="12" width="2" height="104" fill="#2a3c55"/>
 
     <!-- Tab rows: the active one carries the accent, the rest are muted. -->
     <rect x="16" y="30" width="26" height="12" rx="6" fill="url(#accent)"/>
-    <rect x="16" y="50" width="26" height="12" rx="6" fill="#5d5280"/>
-    <rect x="16" y="70" width="26" height="12" rx="6" fill="#493f66"/>
+    <rect x="16" y="50" width="26" height="12" rx="6" fill="#3f5573"/>
+    <rect x="16" y="70" width="26" height="12" rx="6" fill="#2f4460"/>
   </g>
 
   <!-- Prompt chevron and cursor, the universal shorthand for a terminal. -->
   <path d="M66 51 L79 64 L66 77"
-        fill="none" stroke="#e8e2f7" stroke-width="9"
+        fill="none" stroke="#dde6f4" stroke-width="9"
         stroke-linecap="round" stroke-linejoin="round"/>
   <rect x="86" y="70" width="22" height="8" rx="4" fill="url(#accent)"/>