diff --git a/sass/init/_variables.scss b/sass/init/_variables.scss
index b94fbd2..d3f31c0 100644
--- a/sass/init/_variables.scss
+++ b/sass/init/_variables.scss
@@ -74,6 +74,9 @@ $impact:          Impact, 'Arial Narrow', Helvetica, sans-serif;
 $lucida:          'Lucida Grande', 'Lucida Sans Unicode', Lucida, Verdana, sans-serif;
 $futura:          Futura, 'Century Gothic', AppleGothic, sans-serif;
 
+// System-ui font stack.
+$system-ui:       system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif;
+
 // Monospace font stacks.
 // For an explanation of why "sans-serif" is at the end of this list, see
 // http://meyerweb.com/eric/thoughts/2010/02/12/fixed-monospace-sizing/