Only center imgs in figures

Change-Id: I756d9ecc885f51b39a26418bd008581c4593672a
diff --git a/inst/rmarkdown/templates/posterdown_ids/resources/template.html b/inst/rmarkdown/templates/posterdown_ids/resources/template.html
index bf6c698..9e01167 100644
--- a/inst/rmarkdown/templates/posterdown_ids/resources/template.html
+++ b/inst/rmarkdown/templates/posterdown_ids/resources/template.html
@@ -219,7 +219,7 @@
 font-weight: normal;
 margin-block-start: 0.2em;
 }
-img {
+.figure > img {
 margin-top: 0;
 margin-bottom: 0;
 margin-left: auto;