add github button to homepage

Author: isabella

crates/www/layouts/document.rs

@@ -33,6 +33,12 @@ impl Component for Document {
 				meta()
 					.attribute("content", "Tangram makes it easy for programmers to train, deploy, and monitor machine learning models.")
 					.attribute("name", "description"),
+			)
+			.child(
+				script()
+					.attribute("async", true)
+					.attribute("defer", true)
+					.attribute("src", "https://buttons.github.io/buttons.js"),
 			);
 		let client_script = self.client.map(|client| {
 			let paths = sunfish::client_paths(client);

crates/www/layouts/layout.rs

@@ -24,9 +24,22 @@ struct Topbar;
 
 impl Component for Topbar {
 	fn into_node(self) -> Node {
+		let gh_button = a()
+			.class("github-button")
+			.class("link")
+			.style("color", "var(--text-color)")
+			.href("https://github.com/tangramdotdev/tangram")
+			.attribute(
+				"data-color-scheme",
+				"no-preference: light; light: light; dark: dark;",
+			)
+			.attribute("data-size", "large")
+			.attribute("data-show-count", "true")
+			.attribute("aria-label", "Star tangramdotdev/tangram on GitHub")
+			.child("GitHub");
 		let topbar_items = vec![
 			ui::TopbarItem {
-				element: None,
+				element: Some(gh_button.into_node()),
 				href: "https://github.com/tangramdotdev/tangram".to_owned(),
 				title: "GitHub".to_owned(),
 			},

crates/www/pages/index/server/tuning.rs

@@ -220,11 +220,11 @@ impl Component for Tuning {
 		let title = div()
 			.class("index-step-title")
 			.child("Tune your model to get the best performance.");
-		let text = ui::Markdown::new(ui::doc!(
+		let text = div().class("index-step-text").child(ui::Markdown::new(ui::doc!(
 			r#"
 				Tune binary classification models to your preferred tradeoff between precision and recall. To use your selected threshold, update the `predict` call in your code.
 			"#
-		).into());
+		).into()));
 		let left = div().child(title).child(text);
 		let right = ui::Window::new().child(Dehydrate::new(
 			"tuning",