Extension viewlet high contrast mouse over borders only highlight a single...

Extension viewlet high contrast mouse over borders only highlight a single border for top and bottom entries (fixes #15859)

src/vs/base/browser/ui/list/listWidget.ts

@@ -887,7 +887,7 @@ export class List<T> implements ISpliceable<T>, IDisposable {
 		}
 
 		if (styles.listSelectionOutline) {
-			content.push(`.monaco-list.${this.idPrefix} .monaco-list-row.selected { outline: 1px dotted ${styles.listSelectionOutline}; }`);
+			content.push(`.monaco-list.${this.idPrefix} .monaco-list-row.selected { outline: 1px dotted ${styles.listSelectionOutline}; outline-offset: -1px; }`);
 		}
 
 		if (styles.listFocusOutline) {