diff --git a/src/haz3lweb/www/style/exercise-mode.css b/src/haz3lweb/www/style/exercise-mode.css
index dcb2ff37ad..1dac832e86 100644
--- a/src/haz3lweb/www/style/exercise-mode.css
+++ b/src/haz3lweb/www/style/exercise-mode.css
@@ -29,11 +29,11 @@
   text-transform: uppercase;
 }
 
-#main.Exercises .cell {
+#main.Exercises .cell.unlocked {
   border-left: 1px solid var(--cell-exercises-border);
 }
 
-#main.Exercises .cell:has(.code-editor.selected) {
+#main.Exercises .cell.unlocked:has(.code-editor.selected) {
   border-left: 1px solid var(--cell-selected-accent);
   background-color: var(--cell-active);
 }