fix: implement progressbar background and fill rendering as rounded quads

 src/widget/display/progress_bar.rs | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/widget/display/progress_bar.rs b/src/widget/display/progress_bar.rs
index d6f1583..62331d5 100644
--- a/src/widget/display/progress_bar.rs
+++ b/src/widget/display/progress_bar.rs
@@ -34,10 +34,31 @@ impl Element for ProgressBar {
 
     fn color(&self) -> [f32; 4] { colors::progress_bg() }
 
-    fn extra_quads(&self) -> Vec<(f32, f32, f32, f32, [f32; 4])> {
+    fn corner_radius(&self) -> f32 {
+        crate::layout::slider_corner_radius()
+    }
+
+    fn rounded_corners(&self) -> (bool, bool, bool, bool) {
+        (true, true, true, true)
+    }
+
+    fn all_rounded_quads(&self, _ctx: &UiContext) -> Vec<(f32, f32, f32, f32, f32, [f32; 4], (bool, bool, bool, bool))> {
+        if !self.visible() {
+            return Vec::new();
+        }
+        let mut quads = Vec::new();
         let top = self.base.label_offset();
         let visual_h = self.base.h - top;
+        let radius = self.corner_radius();
+        
+        // Progress bar background
+        quads.push((self.base.x, self.base.y + top, self.base.w, visual_h, radius, colors::progress_bg(), (true, true, true, true)));
+        
+        // Progress fill
         let fill_w = self.base.w * self._value.clamp(0.0, 1.0);
-        vec![(self.base.x, self.base.y + top, fill_w, visual_h, colors::progress_fill())]
+        if fill_w > 0.0 {
+            quads.push((self.base.x, self.base.y + top, fill_w, visual_h, radius.min(visual_h / 2.0), colors::progress_fill(), (true, true, true, true)));
+        }
+        quads
     }
 }