Add guideline to last step of the <Steps> component (#2051)

Co-authored-by: Chris Swithinbank <357379+delucis@users.noreply.github.com>
Co-authored-by: Chris Swithinbank <swithinbank@gmail.com>

.changeset/swift-laws-yawn.md

@@ -0,0 +1,14 @@
+---
+'@astrojs/starlight': minor
+---
+
+Adds a guideline to the last step of the `<Steps>` component.
+
+If you want to preserve the previous behaviour and hide the guideline on final steps, you can add the following custom CSS to your site:
+
+```css
+/* Hide the guideline for the final step in <Steps> lists. */
+.sl-steps > li:last-of-type::after {
+  background: transparent;
+}
+```

packages/starlight/user-components/Steps.astro

@@ -51,7 +51,7 @@ const { html } = processSteps(content);
 	}
 
 	/* Vertical guideline linking list numbers. */
-	.sl-steps > li:not(:last-of-type)::after {
+	.sl-steps > li::after {
 		--guide-width: 1px;
 		content: '';
 		position: absolute;