diff --git a/src/stylesheets/base.css b/src/stylesheets/base.css
index 3d46dfa..1632468 100644
--- a/src/stylesheets/base.css
+++ b/src/stylesheets/base.css
@@ -42,6 +42,7 @@
 	--_gap-half: calc(var(--_gap) / 2);
 	--_wide-screen: 1400px;
 	--_small-screen: 800px;
+	--_readable-screen: max(80dvw, var(--_small-screen));
 
 	/* color */
 	--_accent-color: var(--lime-6);