maybe fix relative len for sized span

src/core/span.rs

@@ -51,7 +51,7 @@ impl Widget for Span {
         let dir_len = if total.ratio != 0.0 {
             ctx.size.axis(axis)
         } else {
-            total.fixed + total.relative * ctx.screen_size.axis(axis)
+            total.fixed + total.relative * ctx.size.axis(axis)
         };
         Vec2::from_axis(axis, dir_len, total.max_sized)
     }