Support imageMaxHeight in new interop threads

Bug: twpowertools:96
Change-Id: Ic8f695d06e06defafda420b91d4fa1007b00f287
diff --git a/src/static/css/image_max_height.css b/src/static/css/image_max_height.css
index 2e9b48b..2463945 100644
--- a/src/static/css/image_max_height.css
+++ b/src/static/css/image_max_height.css
@@ -1,5 +1,6 @@
 ec-question .body img,
-    ec-message .body img {
+    ec-message .body img,
+    .scTailwindThreadPostcontentroot img {
   /* "Max height = full height - 2 * height of the header" */
   max-height: calc(100vh - 2*64px);
 }