--- a/devtools/client/themes/webconsole.css
+++ b/devtools/client/themes/webconsole.css
@@ -411,16 +411,17 @@ html #webconsole-notificationbox {
   /* Always allow scrolling on input - it auto expands in js by setting height,
      but don't want it to get bigger than the window. 24px = toolbar height. */
   max-height: calc(90vh - 24px);
   background-image: var(--theme-command-line-image);
   background-repeat: no-repeat;
   background-size: 16px 16px;
   background-position: 4px 50%;
   color: var(--theme-content-color1);
+  box-sizing: border-box;
 }
 
 .jsterm-complete-node {
   color: var(--theme-comment);
 }
 
 .theme-light .jsterm-input-container {
   /* For light theme use a white background for the input - it looks better