Update default color for cell editor bg (Fixes microsoft#133699)

Author: Miguel Solorio

src/vs/workbench/contrib/notebook/browser/notebookEditorWidget.ts

@@ -35,7 +35,7 @@ import { ILayoutService } from 'vs/platform/layout/browser/layoutService';
 import { ITelemetryService } from 'vs/platform/telemetry/common/telemetry';
 import { contrastBorder, diffInserted, diffRemoved, editorBackground, errorForeground, focusBorder, foreground, iconForeground, listInactiveSelectionBackground, registerColor, scrollbarSliderActiveBackground, scrollbarSliderBackground, scrollbarSliderHoverBackground, textBlockQuoteBackground, textBlockQuoteBorder, textLinkActiveForeground, textLinkForeground, textPreformatForeground, toolbarHoverBackground, transparent } from 'vs/platform/theme/common/colorRegistry';
 import { IThemeService, registerThemingParticipant } from 'vs/platform/theme/common/themeService';
-import { PANEL_BORDER } from 'vs/workbench/common/theme';
+import { PANEL_BORDER, SIDE_BAR_BACKGROUND } from 'vs/workbench/common/theme';
 import { debugIconStartForeground } from 'vs/workbench/contrib/debug/browser/debugColors';
 import { CellEditState, CellFocusMode, IActiveNotebookEditorDelegate, ICellOutputViewModel, ICellViewModel, ICommonCellInfo, IDisplayOutputLayoutUpdateRequest, IFocusNotebookCellOptions, IGenericCellViewModel, IInsetRenderOutput, INotebookCellOutputLayoutInfo, INotebookDeltaDecoration, INotebookEditorContribution, INotebookEditorContributionDescription, INotebookEditorCreationOptions, INotebookEditorDelegate, INotebookEditorMouseEvent, INotebookEditorOptions, NotebookCellStateChangedEvent, NotebookLayoutChangedEvent, NotebookLayoutInfo, NOTEBOOK_EDITOR_EDITABLE, NOTEBOOK_EDITOR_FOCUSED, NOTEBOOK_OUTPUT_FOCUSED, RenderOutputType } from 'vs/workbench/contrib/notebook/browser/notebookBrowser';
 import { NotebookDecorationCSSRules, NotebookRefCountedStyleSheet } from 'vs/workbench/contrib/notebook/browser/viewParts/notebookEditorDecorations';
@@ -2713,8 +2713,8 @@ export const cellSymbolHighlight = registerColor('notebook.symbolHighlightBackgr
 }, nls.localize('notebook.symbolHighlightBackground', "Background color of highlighted cell"));
 
 export const cellEditorBackground = registerColor('notebook.cellEditorBackground', {
-	light: transparent(foreground, 0.04),
-	dark: transparent(foreground, 0.04),
+	light: SIDE_BAR_BACKGROUND,
+	dark: SIDE_BAR_BACKGROUND,
 	hc: null
 }, nls.localize('notebook.cellEditorBackground', "Cell editor background color."));