diff --git a/core/themes/seven/css/components/dropzone.css b/core/themes/seven/css/components/dropzone.css
index eca8d7c401..205e5f865c 100644
--- a/core/themes/seven/css/components/dropzone.css
+++ b/core/themes/seven/css/components/dropzone.css
@@ -4,6 +4,7 @@
 .dropzone {
   position: relative;
   display: flex;
+  box-sizing: border-box;
   width: 100%;
   height: 100%;
   border: 1px solid #bfbfbf;