GUAC-694: Do not trust fixed positioning for main display and text input UI.

guacamole/src/main/webapp/styles/client.css

@@ -25,6 +25,7 @@ body {
     font-family: FreeSans, Helvetica, Arial, sans-serif;
     padding: 0;
     margin: 0;
+    overflow: hidden;
 }
 
 img {
@@ -115,11 +116,7 @@ div.dialog p {
 
 div#main {
     overflow: auto;
-    position: fixed;
-    top: 0;
-    left: 0;
-    bottom: 0;
-    right: 0;
+    position: absolute;
 }
 
 div.displayOuter {
@@ -681,10 +678,7 @@ p.hint {
 
 #text-input {
     display: none;
-    position: fixed;
-    left: 0;
-    bottom: 0;
-    width: 100%;
+    position: absolute;
 
     border-top: 1px solid rgba(0, 0, 0, 0.5);
     background: #CDA;