--- a/devtools/client/themes/responsivedesign.inc.css
+++ b/devtools/client/themes/responsivedesign.inc.css
@@ -162,16 +162,20 @@
 .devtools-responsiveui-toolbar:-moz-locale-dir(rtl) > *:last-child {
   margin-left: 0;
 }
 
 .devtools-responsiveui-close {
   list-style-image: url("chrome://devtools/skin/images/close.svg");
 }
 
+.devtools-responsiveui-close > image {
+  filter: invert(1);
+}
+
 .devtools-responsiveui-rotate {
   list-style-image: url("chrome://devtools/skin/images/responsivemode/responsiveui-rotate.png");
 }
 
 @media (min-resolution: 1.1dppx) {
   .devtools-responsiveui-rotate {
     list-style-image: url("chrome://devtools/skin/images/responsivemode/responsiveui-rotate@2x.png");
   }