Handle bottom margin on the @page level

The other options are not reliable

Change-Id: I5f5eee937e8b062bca7ddf24a41163c0818ed2d7
diff --git a/inst/rmarkdown/templates/posterdown_html/resources/template.html b/inst/rmarkdown/templates/posterdown_html/resources/template.html
index aaa073b..9b99668 100644
--- a/inst/rmarkdown/templates/posterdown_html/resources/template.html
+++ b/inst/rmarkdown/templates/posterdown_html/resources/template.html
@@ -48,7 +48,7 @@
 @import url('//korap.ids-mannheim.de/font/fira-condensed.css');
 @page {
 size: $if(poster_width)$$poster_width$$else$841mm$endif$ $if(poster_height)$$poster_height$$else$1189mm$endif$;
-margin: 0;
+margin: 0 0 2.54cm 0;
 padding: 0;
 }
 body {
@@ -161,13 +161,15 @@
 /*width=82.4%*/
 margin-right: 2cm;
 padding-right: 0.5em;
-margin-bottom: 2.54cm;
-height: -webkit-fill-available;
-height: -moz-available;
-height: fill-available;
+height: 100%;
 color: $if(body_textcol)$$body_textcol$$else$#000000$endif$;
 background-color: $if(body_bgcol)$$body_bgcol$$else$#ffffff$endif$;
 }
+@media print {
+  @page { margin: 0 0 2.54cm 0; }
+  body { margin: 0 0 2.54cm 0;}
+}
+
 .poster_title h1 {
 font-size: $if(title_textsize)$$title_textsize$$else$64pt$endif$;
 margin: inherit;