fix: editor shadow appears under the selected line background when horizontal scroll is active (#5020)

Co-authored-by: Zakhar Kozlov <zakharkv@amazon.com>

Author: InspiredGuy

Readme.md

@@ -152,7 +152,7 @@ npm run test
 
 You can also run the tests in your browser by serving:
 
-    http://localhost:8888/lib/ace/test/tests.html
+    http://localhost:8888/src/test/tests.html
 
 This makes debugging failing tests way more easier.
 

src/css/editor.css.js

@@ -93,8 +93,15 @@ styles.join("\\n")
     right: 0;
 }
 
-.ace_scroller.ace_scroll-left {
+.ace_scroller.ace_scroll-left:after {
+    content: "";
+    position: absolute;
+    top: 0;
+    right: 0;
+    bottom: 0;
+    left: 0;
     box-shadow: 17px 0 16px -16px rgba(0, 0, 0, 0.4) inset;
+    pointer-events: none;
 }
 
 .ace_gutter-cell {