Calculate ClientWebView to include HTML element margins.

* ui/client-web-view.js (PageState::getPreferredHeight): Compute and use
  top and bottom when determining the height value.

* ui/conversation-web-view.css: Remove onerous style defaults now we
  can deal with HTML elements with margins.

ui/client-web-view.js

@@ -53,7 +53,17 @@ PageState.prototype = {
         }, true);
     },
     getPreferredHeight: function() {
-        return window.document.documentElement.offsetHeight;
+        let html = window.document.documentElement;
+        let height = html.offsetHeight;
+        let computed = window.getComputedStyle(html);
+        let top = computed.getPropertyValue('margin-top');
+        let bot = computed.getPropertyValue('margin-bottom');
+
+        return (
+            height
+                + parseInt(top.substring(0, top.length - 2))
+                + parseInt(bot.substring(0, bot.length - 2))
+        );
     },
     loaded: function() {
         this.isLoaded = true;

ui/conversation-web-view.css

@@ -7,33 +7,15 @@
  */
 
 * {
-  transition: height 0.25s;
-}
-
-html {
-  /* Trigger CSS 2.1 § 10.6.7 to get a shrink-wrapped height. */
-  position: absolute !important;
-  top: 0 !important;
-  left: 0 !important;
-  bottom: auto !important;
-  width: 100% !important;
-  height: auto !important;
-
-  /* Lock down the box enough so we don't get an incrementally
-     expanding web view */
-  box-sizing: border-box !important;
-  margin: 0 !important;
-  border: 0 !important;
-  padding: 0;
-
-  /* Never show scroll bars */
-  overflow: hidden;
+  transition: height 0.25s !important;
 }
 
 body {
-  margin: 0;
+  margin: 12px;
   border: 0;
-  padding: 12px;
+  padding: 0;
+
+  /* XXX for plain text only? */
   overflow-wrap: break-word !important;
 }
 
@@ -61,7 +43,6 @@ blockquote {
   padding: 0 8px;
 }
 
-
 pre {
   white-space: pre-wrap;
 }