add sizable trait

crates/theme/src/system.rs

@@ -55,7 +55,12 @@ pub struct SystemTheme {
     pub variant: ThemeVariant,
     pub accent: Option<Hsla>,
     pub palette: PartialPalette,
+    /// The platform's stated control corner radius, if it has one.
     pub control_radius: Option<Pixels>,
+    /// The platform's stated text-field height, if it has one.
+    pub input_height: Option<Pixels>,
+    /// The platform's native root font size, if it has one.
+    pub root_font_size: Option<Pixels>,
     pub accessibility: AccessibilityPreferences,
     pub source: SourceKind,
 }
@@ -67,6 +72,8 @@ impl SystemTheme {
             accent: None,
             palette: PartialPalette::default(),
             control_radius: None,
+            input_height: None,
+            root_font_size: None,
             accessibility: AccessibilityPreferences::default(),
             source: SourceKind::Fallback,
         }