diff --git a/src/usercontent/index.js b/src/usercontent/index.ts
similarity index 55%
rename from src/usercontent/index.js
rename to src/usercontent/index.ts
index c03126ec80..df551e88e6 100644
--- a/src/usercontent/index.js
+++ b/src/usercontent/index.ts
@@ -1,5 +1,5 @@
 let hasCalled = false;
-function remoteRender(event) {
+function remoteRender(event: MessageEvent): void {
     const data = event.data;
 
     // If we're handling secondary calls, start from scratch
@@ -8,13 +8,14 @@ function remoteRender(event) {
     }
     hasCalled = true;
 
-    const img = document.createElement("span"); // we'll mask it as an image
+    const img: HTMLSpanElement = document.createElement("span"); // we'll mask it as an image
     img.id = "img";
 
-    const a = document.createElement("a");
+    const a: HTMLAnchorElement = document.createElement("a");
     a.id = "a";
     a.rel = "noreferrer noopener";
     a.download = data.download;
+    // @ts-ignore
     a.style = data.style;
     a.style.fontFamily = "Arial, Helvetica, Sans-Serif";
     a.href = window.URL.createObjectURL(data.blob);
@@ -23,24 +24,24 @@ function remoteRender(event) {
 
     // Apply image style after so we can steal the anchor's colour.
     // Style copied from a rendered version of mx_MFileBody_download_icon
-    img.style = (data.imgStyle || "" +
-        "width: 12px; height: 12px;" +
-        "-webkit-mask-size: 12px;" +
-        "mask-size: 12px;" +
-        "-webkit-mask-position: center;" +
-        "mask-position: center;" +
-        "-webkit-mask-repeat: no-repeat;" +
-        "mask-repeat: no-repeat;" +
-        "display: inline-block;") + "" +
-
-        // Always add these styles
-        `-webkit-mask-image: url('${data.imgSrc}');` +
-        `mask-image: url('${data.imgSrc}');` +
-        `background-color: ${a.style.color};`;
+    if (data.imgStyle) {
+        // @ts-ignore
+        img.style = data.imgStyle;
+    } else {
+        img.style.width = "12px";
+        img.style.height = "12px";
+        img.style.webkitMaskSize = "12px";
+        img.style.webkitMaskPosition = "center";
+        img.style.webkitMaskRepeat = "no-repeat";
+        img.style.display = "inline-block";
+        img.style.webkitMaskImage = `url('${data.imgSrc}')`;
+        img.style.backgroundColor = `${a.style.color}`;
+    }
 
     const body = document.body;
     // Don't display scrollbars if the link takes more than one line to display.
-    body.style = "margin: 0px; overflow: hidden";
+    body.style .margin = "0px";
+    body.style.overflow = "hidden";
     body.appendChild(a);
 
     if (event.data.auto) {
@@ -48,7 +49,7 @@ function remoteRender(event) {
     }
 }
 
-window.onmessage = function(e) {
+window.onmessage = function(e: MessageEvent): void {
     if (e.origin === window.location.origin) {
         if (e.data.blob) remoteRender(e);
     }