diff --git a/viewer.ts b/viewer.ts
index 1111111..3333333 100644
--- a/viewer.ts
+++ b/viewer.ts
@@ -1,8 +1,24 @@
-const renderer = 'text'
+const renderer = 'highlight.js'
+
+type PreviewMode = 'url' | 'file'
+
 export default renderer

-export function open(url: string) {
-  return fetch(url)
+export async function open(url: string, mode: PreviewMode = 'url') {
+  const response = await fetch(url, { credentials: 'include' })
+  if (!response.ok) {
+    throw new Error(`Preview download failed: ${response.status}`)
+  }
+
+  const blob = await response.blob()
+  if (mode === 'file') {
+    const filename = decodeURIComponent(url.split('/').pop() || 'preview.bin')
+    return new File([blob], filename, { type: blob.type })
+  }
+
+  return blob
 }
diff --git a/styles.css b/styles.css
index aaaaaaa..bbbbbbb 100644
--- a/styles.css
+++ b/styles.css
@@ -4,6 +4,9 @@
 .preview-shell {
   min-height: 100vh;
   overflow: hidden;
+  display: grid;
+  grid-template-columns: minmax(260px, 320px) minmax(0, 1fr);
+  background: #f6f8fb;
 }