Add CSS rules for guestbook replies feature

public/css/index.css

@@ -1060,6 +1060,26 @@ article.post {
 .guestbooks___input-container br {
 	display: none;
 }
+.guestbook-message-reply {
+	border-left: var(--border-details);
+	margin-left: var(--space-l);
+	margin-top: calc(var(--space-s) * -1);
+	opacity: 0.9;
+	padding-left: var(--space-s);
+	font-style: italic;
+	& blockquote {
+		margin-left: 0;
+	}
+	& blockquote::before {
+		content: "";
+	}
+	& p::before {
+		content: "Reply from ";
+		font-family: var(--meta-font-family);
+		font-size: var(--meta-font-size);
+		font-variation-settings: var(--meta-font-variation-settings);
+	}
+}
 
 /* Add fleuron after <p> in article when footnotes are present */
 p:has(+ hr.footnotes-sep):after {