Style titlebar via theme and give it a bottom border

Co-Authored-By: Max Brunsfeld <maxbrunsfeld@gmail.com>

zed/assets/themes/_base.toml

@@ -4,6 +4,9 @@ base = { family = "Inconsolata", size = 14 }
 [workspace]
 background = "$surface.0"
 
+[workspace.titlebar]
+border = { width = 1, bottom = true, color = "$surface.1" }
+
 [workspace.tab]
 text = "$text.2"
 padding = { left = 10, right = 10 }

zed/src/theme.rs

@@ -33,6 +33,7 @@ pub struct SyntaxTheme {
 #[derive(Deserialize)]
 pub struct Workspace {
     pub background: Color,
+    pub titlebar: ContainerStyle,
     pub tab: Tab,
     pub active_tab: Tab,
     pub sidebar: Sidebar,

zed/src/workspace.rs

@@ -952,7 +952,11 @@ impl View for Workspace {
         Container::new(
             Flex::column()
                 .with_child(
-                    ConstrainedBox::new(Empty::new().boxed())
+                    ConstrainedBox::new(
+                        Container::new(Empty::new().boxed())
+                            .with_style(&settings.theme.workspace.titlebar)
+                            .boxed(),
+                    )
                     .with_height(32.)
                     .named("titlebar"),
                 )