Try to make sure that the full height is used

Change-Id: Ib0d48b213a77eb410ddf839bab7b22071febc71a
diff --git a/inst/rmarkdown/templates/posterdown_ids/resources/template.html b/inst/rmarkdown/templates/posterdown_ids/resources/template.html
index 9b99668..5428f69 100644
--- a/inst/rmarkdown/templates/posterdown_ids/resources/template.html
+++ b/inst/rmarkdown/templates/posterdown_ids/resources/template.html
@@ -162,6 +162,9 @@
 margin-right: 2cm;
 padding-right: 0.5em;
 height: 100%;
+height: -moz-available;          /* WebKit-based browsers will ignore this. */
+height: -webkit-fill-available;  /* Mozilla-based browsers will ignore this. */
+height: fill-available;
 color: $if(body_textcol)$$body_textcol$$else$#000000$endif$;
 background-color: $if(body_bgcol)$$body_bgcol$$else$#ffffff$endif$;
 }