diff --git a/src/components/editor/callout-node.tsx b/src/components/editor/callout-node.tsx
index f9285f57..0b22b280 100644
--- a/src/components/editor/callout-node.tsx
+++ b/src/components/editor/callout-node.tsx
@@ -25,12 +25,14 @@ export type SerializedCalloutNode = Spread<
 >;
 
 const VARIANT_CLASSES: Record<CalloutVariant, string> = {
-  info: "bg-muted",
-  warning: "bg-muted",
-  success: "bg-muted",
-  error: "bg-muted",
+  info: "border-l-accent bg-muted",
+  warning: "border-l-code-type bg-muted",
+  success: "border-l-code-string bg-muted",
+  error: "border-l-destructive bg-muted",
 };
 
+const BASE_CLASSES = "mt-3 flex gap-3 border-l-2 p-4 text-sm";
+
 export class CalloutNode extends ElementNode {
   __emoji: string;
   __variant: CalloutVariant;
@@ -69,13 +71,26 @@ export class CalloutNode extends ElementNode {
 
   createDOM(): HTMLElement {
     const div = document.createElement("div");
-    div.className = `mt-3 flex gap-3 p-4 text-sm ${VARIANT_CLASSES[this.__variant]}`;
+    div.className = `${BASE_CLASSES} ${VARIANT_CLASSES[this.__variant]}`;
+
+    const emojiSpan = document.createElement("span");
+    emojiSpan.className = "callout-emoji select-none text-lg shrink-0";
+    emojiSpan.contentEditable = "false";
+    emojiSpan.textContent = this.__emoji;
+    div.appendChild(emojiSpan);
+
     return div;
   }
 
   updateDOM(prevNode: CalloutNode, dom: HTMLElement): boolean {
     if (prevNode.__variant !== this.__variant) {
-      dom.className = `mt-3 flex gap-3 p-4 text-sm ${VARIANT_CLASSES[this.__variant]}`;
+      dom.className = `${BASE_CLASSES} ${VARIANT_CLASSES[this.__variant]}`;
+    }
+    if (prevNode.__emoji !== this.__emoji) {
+      const emojiSpan = dom.querySelector(".callout-emoji");
+      if (emojiSpan) {
+        emojiSpan.textContent = this.__emoji;
+      }
     }
     return false;
   }
diff --git a/src/components/editor/callout-plugin.tsx b/src/components/editor/callout-plugin.tsx
index b5fcc2ff..8c6e0f1f 100644
--- a/src/components/editor/callout-plugin.tsx
+++ b/src/components/editor/callout-plugin.tsx
@@ -3,7 +3,6 @@
 import { useEffect } from "react";
 import { useLexicalComposerContext } from "@lexical/react/LexicalComposerContext";
 import {
-  $getNodeByKey,
   $getSelection,
   $insertNodes,
   $isRangeSelection,
@@ -29,7 +28,6 @@ export function CalloutPlugin(): null {
   const [editor] = useLexicalComposerContext();
 
   useEffect(() => {
-    // Register the CalloutNode if not already registered
     if (!editor.hasNodes([CalloutNode])) {
       throw new Error(
         "CalloutPlugin: CalloutNode not registered on editor. Add it to initialConfig.nodes."
@@ -54,38 +52,5 @@ export function CalloutPlugin(): null {
     );
   }, [editor]);
 
-  // Mutation listener to render emoji prefix in callout DOM
-  useEffect(() => {
-    return editor.registerMutationListener(CalloutNode, (mutations) => {
-      for (const [nodeKey, mutation] of mutations) {
-        if (mutation === "destroyed") continue;
-
-        const dom = editor.getElementByKey(nodeKey);
-        if (!dom) continue;
-
-        editor.read(() => {
-          const node = $getNodeByKey(nodeKey);
-          if (!(node instanceof CalloutNode)) return;
-
-          const emoji = node.getEmoji();
-
-          // querySelector returns Element | null; safe to narrow because we create this span ourselves
-          let emojiSpan = dom.querySelector(
-            ".callout-emoji"
-          ) as HTMLSpanElement | null;
-
-          if (!emojiSpan) {
-            emojiSpan = document.createElement("span");
-            emojiSpan.className = "callout-emoji select-none text-lg shrink-0";
-            emojiSpan.contentEditable = "false";
-            dom.insertBefore(emojiSpan, dom.firstChild);
-          }
-
-          emojiSpan.textContent = emoji;
-        });
-      }
-    });
-  }, [editor]);
-
   return null;
 }
diff --git a/src/components/editor/design-spec-compliance.test.ts b/src/components/editor/design-spec-compliance.test.ts
index 721dae30..6070ebb9 100644
--- a/src/components/editor/design-spec-compliance.test.ts
+++ b/src/components/editor/design-spec-compliance.test.ts
@@ -14,8 +14,8 @@ function readSource(relativePath: string): string {
   return readFileSync(resolve(__dirname, relativePath), "utf-8");
 }
 
-describe("callout-plugin design spec compliance", () => {
-  const source = readSource("./callout-plugin.tsx");
+describe("callout-node design spec compliance", () => {
+  const source = readSource("./callout-node.tsx");
 
   it("callout emoji does not use text-base (not in typography scale)", () => {
     // The typography scale does not include text-base. Emoji should use
@@ -32,6 +32,41 @@ describe("callout-plugin design spec compliance", () => {
     );
     expect(emojiClassLine).not.toBeNull();
   });
+
+  it("callout emoji span is created in createDOM, not via mutation listener", () => {
+    // The emoji must render immediately on insert, not asynchronously via
+    // a mutation listener. Verify createDOM creates the emoji span.
+    expect(source).toContain("createDOM");
+    const createDOMIndex = source.indexOf("createDOM");
+    const emojiIndex = source.indexOf("callout-emoji", createDOMIndex);
+    expect(emojiIndex).toBeGreaterThan(createDOMIndex);
+  });
+
+  it("callout uses a left border to distinguish from code blocks", () => {
+    // Design spec: callouts need visual distinction from code blocks.
+    // A colored left border provides this.
+    expect(source).toContain("border-l-2");
+  });
+
+  it("each callout variant has a distinct border color", () => {
+    // All four variants must map to different border color classes
+    const variantBlock = source.match(
+      /VARIANT_CLASSES[\s\S]*?\{([\s\S]*?)\}/
+    );
+    expect(variantBlock).not.toBeNull();
+    const block = variantBlock![1];
+    expect(block).toContain("border-l-accent");
+    expect(block).toContain("border-l-code-type");
+    expect(block).toContain("border-l-code-string");
+    expect(block).toContain("border-l-destructive");
+  });
+
+  it("callout plugin does not use registerMutationListener for emoji", () => {
+    // Emoji rendering moved to createDOM — the plugin should not
+    // manipulate DOM via mutation listeners.
+    const pluginSource = readSource("./callout-plugin.tsx");
+    expect(pluginSource).not.toContain("registerMutationListener");
+  });
 });
 
 describe("editor anchor element", () => {