Improve source code style slightly

Change-Id: I32186e8d7fcfa913e0ba64e7e494bac60ceddc95
diff --git a/inst/rmarkdown/templates/posterdown_ids/resources/template.html b/inst/rmarkdown/templates/posterdown_ids/resources/template.html
index 03bcb9e..b953304 100644
--- a/inst/rmarkdown/templates/posterdown_ids/resources/template.html
+++ b/inst/rmarkdown/templates/posterdown_ids/resources/template.html
@@ -304,7 +304,8 @@
 }
 div.sourceCode {
 background-color: transparent;
-width: $if(codechunk_width)$$codechunk_width$$else$85%$endif$;
+width: $if(codechunk_width)$$codechunk_width$$else$100%$endif$;
+font-size: $if(codechunk_textsize)$$codechunk_textsize$$else$20pt$endif$;
 margin-left: auto;
 margin-right: auto;
 }
@@ -314,8 +315,8 @@
 border-radius: 2mm;
 }
 code {
-font-size: 25pt;
-font-family: monospace;
+font-size: $if(codechunk_textsize)$$codechunk_textsize$$else$20pt$endif$;
+font-family: "Fira Mono", monospace;
 background-color: $if(secondary_colour)$$secondary_colour$24$else$#00808024$endif$;
 color: $if(secondary_colour)$$secondary_colour$$else$#008080$endif$;
 padding: 1.2mm;