Highlight find matches

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

crates/theme/src/theme.rs

@@ -24,6 +24,7 @@ pub struct Theme {
     pub project_panel: ProjectPanel,
     pub selector: Selector,
     pub editor: EditorStyle,
+    pub find: Find,
     pub project_diagnostics: ProjectDiagnostics,
 }
 
@@ -87,6 +88,11 @@ pub struct Tab {
     pub icon_conflict: Color,
 }
 
+#[derive(Clone, Deserialize, Default)]
+pub struct Find {
+    pub match_background: Color,
+}
+
 #[derive(Deserialize, Default)]
 pub struct Sidebar {
     #[serde(flatten)]