diff --git a/src-tauri/Cargo.lock b/src-tauri/Cargo.lock
index d395ae4..e2d2ef3 100644
--- a/src-tauri/Cargo.lock
+++ b/src-tauri/Cargo.lock
@@ -1538,6 +1538,12 @@ dependencies = [
  "pin-project-lite",
 ]
 
+[[package]]
+name = "http-range"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "21dec9db110f5f872ed9699c3ecf50cf16f423502706ba5c72462e28d3157573"
+
 [[package]]
 name = "httparse"
 version = "1.10.1"
@@ -3746,6 +3752,7 @@ dependencies = [
  "gtk",
  "heck 0.5.0",
  "http",
+ "http-range",
  "jni 0.21.1",
  "libc",
  "log",
diff --git a/src-tauri/Cargo.toml b/src-tauri/Cargo.toml
index 3b53021..03756de 100644
--- a/src-tauri/Cargo.toml
+++ b/src-tauri/Cargo.toml
@@ -18,7 +18,7 @@ crate-type = ["staticlib", "cdylib", "rlib"]
 tauri-build = { version = "2", features = [] }
 
 [dependencies]
-tauri = { version = "2", features = ["macos-private-api"] }
+tauri = { version = "2", features = ["macos-private-api", "protocol-asset"] }
 tauri-plugin-single-instance = "2"
 tauri-plugin-opener = "2"
 tauri-plugin-fs = { version = "2", features = ["watch"] }
diff --git a/src-tauri/tauri.conf.json b/src-tauri/tauri.conf.json
index 649f6bf..a987e56 100644
--- a/src-tauri/tauri.conf.json
+++ b/src-tauri/tauri.conf.json
@@ -23,7 +23,11 @@
       }
     ],
     "security": {
-      "csp": null
+      "csp": null,
+      "assetProtocol": {
+        "enable": true,
+        "scope": ["**"]
+      }
     }
   },
   "plugins": {
diff --git a/src/components/overlays/file-preview-overlay.tsx b/src/components/overlays/file-preview-overlay.tsx
index 305600c..3b95548 100644
--- a/src/components/overlays/file-preview-overlay.tsx
+++ b/src/components/overlays/file-preview-overlay.tsx
@@ -1,8 +1,9 @@
 import { useCallback, useEffect, useMemo, useRef, useState } from "react";
+import { convertFileSrc } from "@tauri-apps/api/core";
 import { readFile, readTextFile, stat } from "@tauri-apps/plugin-fs";
 import { openPath } from "@tauri-apps/plugin-opener";
 import { useI18n } from "@/lib";
-import { basename, isSupportedTextPath, previewKindForPath, previewMimeForPath, validatePlainTextFile } from "@/lib";
+import { basename, dirname, htmlDocWithBase, isSupportedTextPath, previewKindForPath, previewMimeForPath, validatePlainTextFile } from "@/lib";
 
 const CLOSE_ICON_SVG = `<svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M18 6 6 18"/><path d="m6 6 12 12"/></svg>`;
 const EYE_ICON_SVG = `<svg width="13" height="13" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.75" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M2 12s3.5-7 10-7 10 7 10 7-3.5 7-10 7-10-7-10-7Z"/><circle cx="12" cy="12" r="3"/></svg>`;
@@ -54,6 +55,13 @@ export function FilePreviewOverlay({ path, onClose, onOpenAsText }: Props) {
   const [size, setSize] = useState<number | null>(null);
   const [errMsg, setErrMsg] = useState("");
 
+  // html previews get a <base> pointing at the file's directory (via the asset
+  // protocol) so relative images/css/scripts resolve.
+  const htmlDoc = useMemo(
+    () => (path && kind === "html" ? htmlDocWithBase(text, convertFileSrc(dirname(path))) : ""),
+    [path, kind, text],
+  );
+
   const urlRef = useRef<string | null>(null);
 
   const revokeUrl = useCallback(() => {
@@ -102,7 +110,7 @@ export function FilePreviewOverlay({ path, onClose, onOpenAsText }: Props) {
           return;
         }
 
-        if (kind === "text") {
+        if (kind === "text" || kind === "html") {
           const check = await validatePlainTextFile(path);
           if (cancelled) return;
           if (!check.ok) {
@@ -151,7 +159,7 @@ export function FilePreviewOverlay({ path, onClose, onOpenAsText }: Props) {
   if (!path) return null;
 
   const title = basename(path);
-  const showOpenAsText = kind === "text" && isSupportedTextPath(path) === false;
+  const showOpenAsText = (kind === "text" || kind === "html") && isSupportedTextPath(path) === false;
 
   return (
     <div
@@ -223,6 +231,13 @@ export function FilePreviewOverlay({ path, onClose, onOpenAsText }: Props) {
           </div>
         ) : kind === "pdf" && url ? (
           <iframe className="mdv-file-viewer__pdf" src={url} title={title} />
+        ) : kind === "html" ? (
+          <iframe
+            className="mdv-file-viewer__html"
+            sandbox="allow-scripts"
+            srcDoc={htmlDoc}
+            title={title}
+          />
         ) : kind === "text" ? (
           <pre className="mdv-file-viewer__text">{text}</pre>
         ) : (
diff --git a/src/lib/index.ts b/src/lib/index.ts
index 7a27d3b..d5c1b43 100644
--- a/src/lib/index.ts
+++ b/src/lib/index.ts
@@ -78,7 +78,7 @@ export {
 } from "./context-bundle";
 export { startWindowDrag } from "./window-drag";
 export { exportPreviewToPdf, PdfExportError } from "./pdf-export";
-export { previewKindForPath, previewMimeForPath, type PreviewKind } from "./preview";
+export { previewKindForPath, previewMimeForPath, htmlDocWithBase, type PreviewKind } from "./preview";
 export { IS_MAC, IS_WINDOWS, IS_LINUX, displayKey, shortcutLabel } from "./platform";
 export {
   pickFolder,
diff --git a/src/lib/preview.ts b/src/lib/preview.ts
index 1dad20d..ccbe3dd 100644
--- a/src/lib/preview.ts
+++ b/src/lib/preview.ts
@@ -3,8 +3,10 @@
  *
  * The sidebar opens `.md/.markdown/.mdx/.csv` in the editor; every other file
  * goes through the preview overlay. `previewKindForPath` decides which renderer
- * the overlay uses. Mime values are webview-native (no parsing library) so the
- * overlay can build blob/data URLs straight from `readFile` bytes.
+ * the overlay uses (`.html/.htm` render in a sandboxed iframe with a `<base>`
+ * pointing at the file's directory via the asset protocol). Mime values are
+ * webview-native (no parsing library) so the overlay can build blob/data URLs
+ * straight from `readFile` bytes.
  */
 
 export type PreviewKind =
@@ -12,6 +14,7 @@ export type PreviewKind =
   | "video"
   | "audio"
   | "pdf"
+  | "html"
   | "office"
   | "text"
   | "unsupported";
@@ -87,8 +90,6 @@ const TEXT_EXT = new Set([
   "properties",
   "env",
   "xml",
-  "html",
-  "htm",
   "css",
   "scss",
   "less",
@@ -170,6 +171,7 @@ export function previewKindForPath(path: string): PreviewKind {
   if (VIDEO_MIME[ext]) return "video";
   if (AUDIO_MIME[ext]) return "audio";
   if (ext === "pdf") return "pdf";
+  if (ext === "html" || ext === "htm") return "html";
   if (OFFICE_EXT.has(ext)) return "office";
   if (TEXT_EXT.has(ext)) return "text";
   if (TEXT_BASENAMES.has(basenameLower(path))) return "text";
@@ -182,3 +184,21 @@ export function previewMimeForPath(path: string): string {
   if (ext === "pdf") return "application/pdf";
   return IMAGE_MIME[ext] ?? VIDEO_MIME[ext] ?? AUDIO_MIME[ext] ?? "";
 }
+
+/**
+ * Inject a `<base href>` into an html document so the previewed file resolves
+ * relative resources (images, css, scripts) against its own directory.
+ * `baseHref` is a `convertFileSrc()` asset URL of that directory. An existing
+ * `<base>` in the document would lose (the first one wins), so local files
+ * keep working.
+ */
+export function htmlDocWithBase(html: string, baseHref: string): string {
+  const href = baseHref.endsWith("/") ? baseHref : `${baseHref}/`;
+  const base = `<base href="${href.replace(/"/g, "&quot;")}">`;
+  const head = /<head[^>]*>/i.exec(html);
+  if (head) {
+    const at = head.index + head[0].length;
+    return html.slice(0, at) + base + html.slice(at);
+  }
+  return base + html;
+}
diff --git a/src/styles/overlays/file-preview.css b/src/styles/overlays/file-preview.css
index 5ab8008..5ad3566 100644
--- a/src/styles/overlays/file-preview.css
+++ b/src/styles/overlays/file-preview.css
@@ -276,6 +276,16 @@ html.is-mac .mdv-file-viewer__toolbar {
   background: var(--surface);
 }
 
+/* html — pages assume a white canvas, so don't inherit the app theme. */
+.mdv-file-viewer__html {
+  position: absolute;
+  inset: 0;
+  width: 100%;
+  height: 100%;
+  border: 0;
+  background: #fff;
+}
+
 /* text */
 .mdv-file-viewer__text {
   position: absolute;
diff --git a/tests/preview.test.ts b/tests/preview.test.ts
index c3f5fb2..51420e5 100644
--- a/tests/preview.test.ts
+++ b/tests/preview.test.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "bun:test";
-import { previewKindForPath, previewMimeForPath } from "../src/lib/preview";
+import { previewKindForPath, previewMimeForPath, htmlDocWithBase } from "../src/lib/preview";
 
 test("classifies images by extension", () => {
   expect(previewKindForPath("a.png")).toBe("image");
@@ -20,6 +20,19 @@ test("classifies pdf", () => {
   expect(previewKindForPath("PAPER.PDF")).toBe("pdf");
 });
 
+test("classifies html for rendered preview", () => {
+  expect(previewKindForPath("index.html")).toBe("html");
+  expect(previewKindForPath("docs/page.HTM")).toBe("html");
+});
+
+test("injects a base href for relative html resources", () => {
+  expect(htmlDocWithBase("<html><head><title>x</title></head></html>", "asset://localhost/a/b"))
+    .toBe('<html><head><base href="asset://localhost/a/b/"><title>x</title></head></html>');
+  // no <head> — prepend
+  expect(htmlDocWithBase("<p>hi</p>", "asset://localhost/a/b/"))
+    .toBe('<base href="asset://localhost/a/b/"><p>hi</p>');
+});
+
 test("classifies office documents as info-card", () => {
   expect(previewKindForPath("report.docx")).toBe("office");
   expect(previewKindForPath("sheet.xlsx")).toBe("office");