diff --git a/src/repixelizer/gui_static/styles.css b/src/repixelizer/gui_static/styles.css
index bbbd1b5..2997b83 100644
--- a/src/repixelizer/gui_static/styles.css
+++ b/src/repixelizer/gui_static/styles.css
@@ -1006,6 +1006,8 @@ select.field-control optgroup {
 
 .editor-surface {
   position: relative;
+  width: 100%;
+  aspect-ratio: 1 / 1;
   min-height: 420px;
   overflow: auto;
   padding: 16px;