tweaks for hc theme

src/vs/base/browser/ui/scrollbar/media/scrollbars.css

@@ -123,7 +123,7 @@
 }
 
 .vs-dark .monaco-scrollable-element .shadow.top {
-	box-shadow: #000 0 6px 6px -6px inset;
+	box-shadow: none;
 }
 
 .vs-dark .monaco-scrollable-element .shadow.left {
@@ -132,4 +132,16 @@
 
 .vs-dark .monaco-scrollable-element .shadow.top.left {
 	box-shadow: #000 6px 6px 6px -6px inset;
+}
+
+.hc-black .monaco-scrollable-element .shadow.top {
+	box-shadow: none;
+}
+
+.hc-black .monaco-scrollable-element .shadow.left {
+	box-shadow: none;
+}
+
+.hc-black .monaco-scrollable-element .shadow.top.left {
+	box-shadow: none;
 }
\ No newline at end of file

src/vs/base/browser/ui/splitview/splitview.css

@@ -87,6 +87,11 @@
 }
 
 /* High Contrast Theming */
+
+.hc-black .monaco-split-view > .split-view-view > .header {
+	background: none;
+}
+
 .hc-black .monaco-split-view > .split-view-view:not(:first-child) > .header {
 	border-top: 1px solid #6FC3DF;
 }

src/vs/editor/browser/viewParts/scrollDecoration/scrollDecoration.css

@@ -14,3 +14,7 @@
 .monaco-editor.vs-dark .scroll-decoration {
 	box-shadow: #000 0 6px 6px -6px inset;
 }
+
+.monaco-editor.hc-black .scroll-decoration {
+	box-shadow: none;
+}
\ No newline at end of file