diff --git a/css/book-layout.css b/css/book-layout.css
new file mode 100644
index 0000000..cf0d92e
--- /dev/null
+++ b/css/book-layout.css
@@ -0,0 +1,156 @@
+/* Reset body to a layout container (book-page.css targets body for page content) */
+html, body {
+  height: 100vh;
+  overflow: hidden;
+  display: flex;
+  flex-direction: column;
+  padding: 0;
+  max-width: unset;
+  margin: 0;
+  background-image: none;
+}
+
+#layout {
+  display: flex;
+  flex: 1;
+  overflow: hidden;
+}
+
+/* ── Sidebar ── */
+#sidebar {
+  width: 270px;
+  flex-shrink: 0;
+  display: flex;
+  flex-direction: column;
+  background: var(--surface);
+  border-right: 1px solid var(--border-bright);
+  overflow: hidden;
+}
+
+#sidebar-header {
+  padding: 14px 16px;
+  background: var(--surface2);
+  border-bottom: 1px solid var(--border-bright);
+  flex-shrink: 0;
+}
+
+#sidebar-header p {
+  font-family: var(--font-mono);
+  font-size: 0.7rem;
+  color: var(--text-dim);
+  margin-top: 4px;
+}
+
+#page-list {
+  flex: 1;
+  overflow-y: auto;
+  list-style: none;
+  padding: 4px 0;
+}
+
+#page-list li button {
+  width: 100%;
+  text-align: left;
+  padding: 6px 14px;
+  background: none;
+  border: none;
+  cursor: pointer;
+  color: var(--text-dim);
+  font-family: var(--font-body);
+  font-size: 0.88rem;
+  display: flex;
+  gap: 10px;
+  align-items: baseline;
+  transition: background 0.15s, color 0.15s;
+}
+
+#page-list li button:hover {
+  background: var(--surface2);
+  color: var(--text);
+}
+
+#page-list li.active button {
+  background: var(--surface3);
+  color: var(--teal);
+}
+
+.page-num {
+  flex-shrink: 0;
+  min-width: 24px;
+  font-family: var(--font-mono);
+  font-size: 0.72rem;
+  color: var(--border-bright);
+}
+
+li.active .page-num {
+  color: var(--teal-dim);
+}
+
+/* ── Main area ── */
+#main {
+  flex: 1;
+  display: flex;
+  flex-direction: column;
+  overflow: hidden;
+}
+
+/* ── Nav bar ── */
+#nav {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  padding: 10px 20px;
+  background: var(--surface);
+  border-bottom: 1px solid var(--border-bright);
+  flex-shrink: 0;
+}
+
+#page-title {
+  flex: 1;
+  text-align: center;
+  font-family: var(--font-display);
+  font-size: 0.65rem;
+  letter-spacing: 0.12em;
+  text-transform: uppercase;
+  color: var(--text);
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+#page-indicator {
+  font-family: var(--font-mono);
+  font-size: 0.72rem;
+  color: var(--text-dim);
+  white-space: nowrap;
+}
+
+/* ── Scrollable content ── */
+#content {
+  flex: 1;
+  overflow-y: auto;
+  background: var(--bg);
+  background-image:
+    radial-gradient(ellipse at 20% 10%, rgba(78,205,196,.04) 0%, transparent 50%),
+    radial-gradient(ellipse at 80% 90%, rgba(201,168,76,.04) 0%, transparent 50%);
+}
+
+/* ── Page sections ── */
+.page-section {
+  max-width: 860px;
+  margin: 0 auto;
+  padding: 32px;
+  border-bottom: 1px solid var(--border);
+}
+
+.page-section:last-child {
+  border-bottom: none;
+  min-height: calc(100vh - 80px);
+}
+
+/* Override book-page.css header rule inside sections */
+.page-section header {
+  border-bottom: 1px solid var(--border);
+  padding-bottom: 0.8em;
+  margin-bottom: 1.4em;
+}
diff --git a/src/BookIndex.jsx b/src/BookIndex.jsx
index 37f304e..d59e69d 100644
--- a/src/BookIndex.jsx
+++ b/src/BookIndex.jsx
@@ -1,164 +1,5 @@
 import React from 'react';
 
-const INLINE_CSS = `
-  /* Reset body to a layout container (book-page.css targets body for page content) */
-  html, body {
-    height: 100vh;
-    overflow: hidden;
-    display: flex;
-    flex-direction: column;
-    padding: 0;
-    max-width: unset;
-    margin: 0;
-    background-image: none;
-  }
-
-  #layout {
-    display: flex;
-    flex: 1;
-    overflow: hidden;
-  }
-
-  /* ── Sidebar ── */
-  #sidebar {
-    width: 270px;
-    flex-shrink: 0;
-    display: flex;
-    flex-direction: column;
-    background: var(--surface);
-    border-right: 1px solid var(--border-bright);
-    overflow: hidden;
-  }
-
-  #sidebar-header {
-    padding: 14px 16px;
-    background: var(--surface2);
-    border-bottom: 1px solid var(--border-bright);
-    flex-shrink: 0;
-  }
-
-  #sidebar-header p {
-    font-family: var(--font-mono);
-    font-size: 0.7rem;
-    color: var(--text-dim);
-    margin-top: 4px;
-  }
-
-  #page-list {
-    flex: 1;
-    overflow-y: auto;
-    list-style: none;
-    padding: 4px 0;
-  }
-
-  #page-list li button {
-    width: 100%;
-    text-align: left;
-    padding: 6px 14px;
-    background: none;
-    border: none;
-    cursor: pointer;
-    color: var(--text-dim);
-    font-family: var(--font-body);
-    font-size: 0.88rem;
-    display: flex;
-    gap: 10px;
-    align-items: baseline;
-    transition: background 0.15s, color 0.15s;
-  }
-
-  #page-list li button:hover {
-    background: var(--surface2);
-    color: var(--text);
-  }
-
-  #page-list li.active button {
-    background: var(--surface3);
-    color: var(--teal);
-  }
-
-  .page-num {
-    flex-shrink: 0;
-    min-width: 24px;
-    font-family: var(--font-mono);
-    font-size: 0.72rem;
-    color: var(--border-bright);
-  }
-
-  li.active .page-num {
-    color: var(--teal-dim);
-  }
-
-  /* ── Main area ── */
-  #main {
-    flex: 1;
-    display: flex;
-    flex-direction: column;
-    overflow: hidden;
-  }
-
-  /* ── Nav bar ── */
-  #nav {
-    display: flex;
-    align-items: center;
-    gap: 10px;
-    padding: 10px 20px;
-    background: var(--surface);
-    border-bottom: 1px solid var(--border-bright);
-    flex-shrink: 0;
-  }
-
-  #page-title {
-    flex: 1;
-    text-align: center;
-    font-family: var(--font-display);
-    font-size: 0.65rem;
-    letter-spacing: 0.12em;
-    text-transform: uppercase;
-    color: var(--text);
-    overflow: hidden;
-    text-overflow: ellipsis;
-    white-space: nowrap;
-  }
-
-  #page-indicator {
-    font-family: var(--font-mono);
-    font-size: 0.72rem;
-    color: var(--text-dim);
-    white-space: nowrap;
-  }
-
-  /* ── Scrollable content ── */
-  #content {
-    flex: 1;
-    overflow-y: auto;
-    background: var(--bg);
-    background-image:
-      radial-gradient(ellipse at 20% 10%, rgba(78,205,196,.04) 0%, transparent 50%),
-      radial-gradient(ellipse at 80% 90%, rgba(201,168,76,.04) 0%, transparent 50%);
-  }
-
-  /* ── Page sections ── */
-  .page-section {
-    max-width: 860px;
-    margin: 0 auto;
-    padding: 32px;
-    border-bottom: 1px solid var(--border);
-  }
-
-  .page-section:last-child {
-    border-bottom: none;
-    min-height: calc(100vh - 80px);
-  }
-
-  /* Override book-page.css header rule inside sections */
-  .page-section header {
-    border-bottom: 1px solid var(--border);
-    padding-bottom: 0.8em;
-    margin-bottom: 1.4em;
-  }
-`;
-
 function buildScript(pageNums) {
   return `
 const PAGES   = [${pageNums.join(',')}];
@@ -253,7 +94,7 @@ export default function BookIndex({ title, logoText, pages }) {
           rel="stylesheet"
         />
         <link rel="stylesheet" href="/css/book-page.css" />
-        <style dangerouslySetInnerHTML={{ __html: INLINE_CSS }} />
+        <link rel="stylesheet" href="/css/book-layout.css" />
       </head>
       <body>
         <header>