feat(FloatingChat): refactor chat width handling to be dynamic; enhance message panel positioning and styling with glass surface effects

src/renderer/globals.css

@@ -184,6 +184,78 @@ body {
   overflow: hidden;
 }
 
+/* ---- Glass Surface (ReactBits-style) ---- */
+/*
+ * Gradient border via padding-box/border-box background split —
+ * most reliable technique in Chromium/Electron; no pseudo-element mask needed.
+ */
+.glass-surface {
+  border: 1px solid transparent;
+  background:
+    /* glass fill — clips to padding-box (inside the border) */
+    rgba(255, 255, 255, 0.55) padding-box,
+    /* gradient border — clips to border-box (the 1px border strip) */
+    linear-gradient(
+      145deg,
+      rgba(255, 255, 255, 0.90) 0%,
+      rgba(200, 195, 205, 0.40) 40%,
+      rgba(200, 195, 205, 0.20) 100%
+    ) border-box;
+  backdrop-filter: blur(24px) saturate(180%);
+  -webkit-backdrop-filter: blur(24px) saturate(180%);
+  box-shadow:
+    0 4px 48px rgba(0, 0, 0, 0.10),
+    0 1px 2px rgba(0, 0, 0, 0.06),
+    inset 0 1px 0 rgba(255, 255, 255, 0.80);
+}
+
+.dark .glass-surface {
+  background:
+    rgba(255, 255, 255, 0.05) padding-box,
+    linear-gradient(
+      145deg,
+      rgba(255, 255, 255, 0.18) 0%,
+      rgba(255, 255, 255, 0.04) 40%,
+      rgba(255, 255, 255, 0.08) 100%
+    ) border-box;
+  box-shadow:
+    0 4px 48px rgba(0, 0, 0, 0.50),
+    0 1px 2px rgba(0, 0, 0, 0.20),
+    inset 0 1px 0 rgba(255, 255, 255, 0.10);
+}
+
+/* Subtle variant — same gradient border, much more transparent fill */
+.glass-surface-subtle {
+  border: 1px solid transparent;
+  background:
+    rgba(255, 255, 255, 0.20) padding-box,
+    linear-gradient(
+      145deg,
+      rgba(255, 255, 255, 0.70) 0%,
+      rgba(200, 195, 205, 0.25) 40%,
+      rgba(200, 195, 205, 0.10) 100%
+    ) border-box;
+  backdrop-filter: blur(16px) saturate(160%);
+  -webkit-backdrop-filter: blur(16px) saturate(160%);
+  box-shadow:
+    0 2px 12px rgba(0, 0, 0, 0.06),
+    inset 0 1px 0 rgba(255, 255, 255, 0.60);
+}
+
+.dark .glass-surface-subtle {
+  background:
+    rgba(255, 255, 255, 0.03) padding-box,
+    linear-gradient(
+      145deg,
+      rgba(255, 255, 255, 0.12) 0%,
+      rgba(255, 255, 255, 0.02) 40%,
+      rgba(255, 255, 255, 0.05) 100%
+    ) border-box;
+  box-shadow:
+    0 2px 12px rgba(0, 0, 0, 0.30),
+    inset 0 1px 0 rgba(255, 255, 255, 0.07);
+}
+
 /* Crepe editor layout */
 .milkdown-container {
   display: flex;