diff --git a/ui/src/app/title-bar/title-bar.ts b/ui/src/app/title-bar/title-bar.ts
index 8cf5f0e..b2277d7 100644
--- a/ui/src/app/title-bar/title-bar.ts
+++ b/ui/src/app/title-bar/title-bar.ts
@@ -28,6 +28,10 @@ import { RpcService } from '../rpc.service';
   selector: 'app-title-bar',
   host: {
     class: 'title-bar electrobun-webkit-app-region-drag',
+    // Published so the FRAME can react: a maximized Win7 window has square
+    // corners. The window root reads this off its own child via :has() rather
+    // than subscribing to windowState a second time — see styles.css.
+    '[class.is-maximized]': 'maximized()',
     '(dblclick)': 'toggle()',
   },
   template: `
diff --git a/ui/src/styles.css b/ui/src/styles.css
index dc4f395..6ccb3ff 100644
--- a/ui/src/styles.css
+++ b/ui/src/styles.css
@@ -615,6 +615,22 @@ body {
   font-family: var(--w7-family);
 }
 
+/* The win7 window is a FRAMELESS, natively transparent window whose only
+   opaque surface is meant to be `.window` — that is the whole premise of the
+   6px rounded frame, since the area outside the radius must let the desktop
+   through. The unlayered `html, body { background: var(--background) }` above
+   broke that premise silently: it painted an opaque rectangle behind the
+   frame, so the rounded corners had an opaque ground filling them in and the
+   window read as a rectangle with a drawn-on curve.
+   Unlayered on purpose, same reason as the font-family rule: the html/body
+   background it overrides is itself unlayered, and unlayered declarations beat
+   every @layer regardless of specificity — a `skinfix` rule could not touch
+   it. Scoped to .win7 so the modern skin keeps its opaque ground. */
+html.win7,
+html.win7 body {
+  background: transparent;
+}
+
 /* Neutralizers live in `skin`, NOT `skinfix`, and this is load-bearing:
    `revert-layer` rolls a property back to the previous LAYER, so from inside
    `skin` it lands on `utilities` (the Tailwind classes already in the
@@ -724,9 +740,12 @@ body {
   }
 
   /* ---- Window frame ----
-     The native window is transparent (chromeOptions in src/bun/windows.ts), so
-     nothing but .window paints an opaque surface — that is what lets the 6px
-     corner radius actually be transparent at the corners.
+     The native window is transparent (chromeOptions in src/bun/windows.ts), and
+     nothing but .window may paint an opaque surface — that is what lets the 6px
+     corner radius actually be transparent at the corners. That invariant is NOT
+     free: html/body paint an opaque background unlayered, and had to be reset
+     to transparent for .win7 (see the rule above @layer skin). Anything else
+     that paints full-bleed will fill the corners the same way.
      NO drop shadow, by request: 7.css's `2px 2px 10px 1px #000000b3` needed a
      margin gutter to fall into and still read heavy against a real desktop, so
      the frame keeps only the inset 1px glass highlight from that shorthand
@@ -741,6 +760,22 @@ body {
     box-shadow: inset 0 0 0 1px #fffa;
   }
 
+  /* A maximized Win7 window has SQUARE corners — the radius only exists to let
+     the desktop show past a floating frame, and a rounded maximized window
+     leaves four notches of desktop in the screen corners.
+     Read off the title bar's own `is-maximized` (title-bar.ts publishes it on
+     its host) with :has(), so the frame reacts without a second windowState
+     subscription. .title-bar is a DIRECT child of .window — app-title-bar
+     carries the class on its host element, which is why `>` holds here.
+     The radius is declared three times in 7.css — on .window and on both the
+     ::before tint and the ::after glass layer — so all three must be zeroed or
+     a rounded pseudo-element still cuts the corner off the square frame. */
+  .win7 .window.w7-frame:has(> .title-bar.is-maximized),
+  .win7 .window.w7-frame:has(> .title-bar.is-maximized)::before,
+  .win7 .window.w7-frame:has(> .title-bar.is-maximized)::after {
+    border-radius: 0;
+  }
+
   /* 7.css's glass layer is `backdrop-filter: blur(4px)` on .window::after —
      but CSS cannot sample the DESKTOP behind a transparent native window
      (there is no backdrop to read), and WebKitGTK paints the unsampleable