--- a/devtools/client/jsonview/css/toolbar.css
+++ b/devtools/client/jsonview/css/toolbar.css
@@ -15,29 +15,29 @@
   background: var(--theme-toolbar-background);
   border-bottom: 1px solid var(--theme-splitter-color);
 }
 
 .toolbar .btn {
   margin-inline-start: 5px;
   color: var(--theme-body-color);
   background: var(--toolbarbutton-background);
-  border: var(--toolbarbutton-border);
+  border: 1px solid var(--toolbarbutton-border-color);
   text-decoration: none;
   display: inline-block;
   text-align: center;
   white-space: nowrap;
   vertical-align: middle;
   cursor: pointer;
   -moz-user-select: none;
   padding: 0 2px;
   border-radius: 2px;
 }
 
 .toolbar .btn:hover {
   background: var(--toolbarbutton-hover-background);
-  border: var(--toolbarbutton-hover-border);
+  border-color: var(--toolbarbutton-hover-border-color);
 }
 
 .toolbar .btn:not([disabled]):hover:active {
   background-color: var(--theme-selection-background-hover);
 }