10583 panel resize icon fix (#10585)

* removed svg, added ::after

* removed unnecessary code

public/img/resize-handle-white.svg

-<?xml version="1.0" standalone="no"?>
-<!-- Generator: Adobe Fireworks CS6, Export SVG Extension by Aaron Beall (http://fireworks.abeall.com) . Version: 0.6.1  -->
-<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
-<svg id="Untitled-Page%201" viewBox="0 0 6 6" style="background-color:#ffffff00" version="1.1"
-	xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" xml:space="preserve"
-	x="0px" y="0px" width="6px" height="6px"
->
-	<g opacity="0.302">
-		<path d="M 6 6 L 0 6 L 0 4.2 L 4 4.2 L 4.2 4.2 L 4.2 0 L 6 0 L 6 6 L 6 6 Z" fill="#FFFFFF"/>
-	</g>
-</svg>
\ No newline at end of file

public/sass/components/_dashboard_grid.scss

-@import "~react-grid-layout/css/styles.css";
-@import "~react-resizable/css/styles.css";
+@import '~react-grid-layout/css/styles.css';
+@import '~react-resizable/css/styles.css';
 
 .panel-in-fullscreen {
   .react-grid-layout {
@@ -40,8 +40,9 @@
 }
 
 .theme-dark {
-  .react-grid-item > .react-resizable-handle {
-    background-image: url("../img/resize-handle-white.svg");
+  .react-grid-item > .react-resizable-handle::after {
+    border-right: 2px solid rgba(255, 255, 255, 0.4);
+    border-bottom: 2px solid rgba(255, 255, 255, 0.4);
   }
 }