demo: layout fixes, sticky removal, style overrides, css-like rendering improvements

examples/demo/styles.glts

@@ -45,8 +45,10 @@ Panel {
     direction: vertical
 }
 
-// ── Header ───────────────────────────────────────────────────────────────────
+// ── Header (sticky — sticks at top of Window when scrolled) ──────────────────
 .header {
+    position: sticky
+    top: 0
     background: $card
     padding: 8px 20px
     border-bottom: 1px solid $border
@@ -60,13 +62,6 @@ Panel {
 }
 
 // ── Layout ───────────────────────────────────────────────────────────────────
-.body-scroll {
-    overflow-y: auto
-    flex-grow: 1
-    padding: 0px
-    gap: 0px
-}
-
 .body {
     direction: horizontal
     padding: 12px
@@ -370,6 +365,8 @@ Slider {
 }
 
 .log-header {
+    position: sticky
+    top: 0
     background: $surface
     padding: 6px 10px
     border-radius: 4px
@@ -379,8 +376,7 @@ Slider {
     width: fill
 }
 
-// Note: position:sticky is not supported by Iced. "Always visible header above
-// scrollable content" is the working pattern.
+// Note: position:sticky approximated via in-flow spacer + overlay (no scroll-tracking)
 // ═══════════════════════════════════════════════════════════════════════════════
 
 // ── Style Inheritance ────────────────────────────────────────────────────────