diff --git a/web_app/static/index.html b/web_app/static/index.html
index 0d56371..b3084d0 100644
--- a/web_app/static/index.html
+++ b/web_app/static/index.html
@@ -116,7 +116,10 @@ <h2 id="contentHeading">Lyrics</h2>
                                 </div>
                             </div>
 
-                            <button id="generateBtn" class="primary-btn">Generate Poster</button>
+                            <button id="generateBtn" class="primary-btn">
+                                <span class="btn-text">Generate Poster</span>
+                                <div class="spinner"></div>
+                            </button>
                         </div>
                     </div>
 
@@ -143,10 +146,6 @@ <h2>Poster</h2>
         </main>
     </div>
     <div id="toastContainer" class="toast-container"></div>
-    <div id="loadingOverlay" class="loading-overlay" style="display: none;">
-        <div class="spinner"></div>
-        <p>Generating your masterpiece...</p>
-    </div>
     <script src="/static/script.js?v=21"></script>
 </body>
 
diff --git a/web_app/static/script.js b/web_app/static/script.js
index 441a4ed..ff0be7a 100644
--- a/web_app/static/script.js
+++ b/web_app/static/script.js
@@ -20,7 +20,6 @@ const startLineInput = document.getElementById('startLine');
 const endLineInput = document.getElementById('endLine');
 const themeInput = document.getElementById('themeInput');
 const fontInput = document.getElementById('fontInput');
-const loadingOverlay = document.getElementById('loadingOverlay');
 
 let currentMetadata = null;
 let searchDebounceTimer = null;
@@ -613,7 +612,15 @@ function handleLyricLineClick(lineNumber) {
 async function generatePoster() {
     if (!currentMetadata) return;
 
-    loadingOverlay.style.display = 'flex';
+    const btnText = generateBtn.querySelector('.btn-text');
+    if (!btnText) return;
+
+    // --- New Loading State Logic ---
+    const originalText = btnText.textContent;
+    generateBtn.classList.add('loading');
+    generateBtn.disabled = true;
+    btnText.textContent = 'Generating...';
+    generateBtn.setAttribute('aria-label', 'Generating poster, please wait.');
 
     const indexingToggle = document.getElementById('indexingToggle');
     const accentToggle = document.getElementById('accentToggle');
@@ -635,8 +642,10 @@ async function generatePoster() {
         const end = endVal;
 
         if (isNaN(start) || isNaN(end) || start >= end) {
-            loadingOverlay.style.display = 'none';
             showToast("Please enter a valid range (Start must be less than End).", "error");
+            // --- Reset Loading State ---
+            generateBtn.classList.remove('loading');
+            generateBtn.disabled = false;
             return;
         }
 
@@ -669,13 +678,17 @@ async function generatePoster() {
             posterContainer.innerHTML = '';
             posterContainer.appendChild(img);
             showDownloadButton(imageUrl, data.filename);
-            loadingOverlay.style.display = 'none';
         };
 
     } catch (error) {
         console.error("Generation failed", error);
         showToast(`Error: ${error.message}`, "error");
-        loadingOverlay.style.display = 'none';
+    } finally {
+        // --- Reset Loading State ---
+        generateBtn.classList.remove('loading');
+        generateBtn.disabled = false;
+        btnText.textContent = originalText;
+        generateBtn.removeAttribute('aria-label');
     }
 }
 
diff --git a/web_app/static/style.css b/web_app/static/style.css
index 468eb76..940d28d 100644
--- a/web_app/static/style.css
+++ b/web_app/static/style.css
@@ -159,6 +159,39 @@ header p {
     background: var(--accent-color);
     color: #1a1a1f;
     width: 100%;
+    position: relative; /* For spinner placement */
+}
+
+.primary-btn .btn-text {
+    transition: opacity 0.2s ease-out;
+}
+
+/* Spinner is inside the button, inheriting from the main .spinner keyframes */
+.primary-btn .spinner {
+    position: absolute;
+    width: 20px;
+    height: 20px;
+    border-width: 2px;
+    border-color: rgba(0, 0, 0, 0.2);
+    border-top-color: #1a1a1f; /* Match button text color */
+    top: 50%;
+    left: 50%;
+    transform: translate(-50%, -50%);
+    display: none; /* Hidden by default */
+}
+
+.primary-btn.loading {
+    cursor: not-allowed;
+    pointer-events: none;
+}
+
+.primary-btn.loading .btn-text {
+    opacity: 0;
+    visibility: hidden; /* Hide from screen readers */
+}
+
+.primary-btn.loading .spinner {
+    display: block;
 }
 
 .primary-btn:hover {