big overhaul of scrollsync and term loading code for UI

src/sh2.less

@@ -672,6 +672,7 @@ body .xterm .xterm-viewport {
     padding-top: 10px;
     padding-right: 0px;
     flex-grow: 1;
+    position: relative;
 
     .line:nth-child(2) {
         padding-top: 1px;

src/sh2.ts

@@ -15,7 +15,9 @@ document.addEventListener("DOMContentLoaded", () => {
     let reactElem = React.createElement(Main, null, null);
     let elem = document.getElementById("app");
     let root = createRoot(elem);
-    root.render(reactElem);
+    setTimeout(() => {
+        root.render(reactElem);
+    }, 500);
 });
 
 (window as any).mobx = mobx;