Button separator color on high-contrast themes (microsoft#155316)

Button separator color on high-contrast themes (Fixes microsoft#155285)

Author: Miguel Solorio

src/vs/platform/theme/common/colorRegistry.ts

@@ -266,7 +266,7 @@ export const checkboxForeground = registerColor('checkbox.foreground', { dark: s
 export const checkboxBorder = registerColor('checkbox.border', { dark: selectBorder, light: selectBorder, hcDark: selectBorder, hcLight: selectBorder }, nls.localize('checkbox.border', "Border color of checkbox widget."));
 
 export const buttonForeground = registerColor('button.foreground', { dark: Color.white, light: Color.white, hcDark: Color.white, hcLight: Color.white }, nls.localize('buttonForeground', "Button foreground color."));
-export const buttonSeparator = registerColor('button.separator', { dark: transparent(buttonForeground, .4), light: transparent(buttonForeground, .4), hcDark: transparent(buttonForeground, .4), hcLight: transparent(buttonForeground, .4) }, nls.localize('buttonSeparator', "Button separator color."));
+export const buttonSeparator = registerColor('button.separator', { dark: transparent(buttonForeground, .4), light: transparent(buttonForeground, .4), hcDark: null, hcLight: transparent(buttonForeground, .4) }, nls.localize('buttonSeparator', "Button separator color."));
 export const buttonBackground = registerColor('button.background', { dark: '#0E639C', light: '#007ACC', hcDark: null, hcLight: '#0F4A85' }, nls.localize('buttonBackground', "Button background color."));
 export const buttonHoverBackground = registerColor('button.hoverBackground', { dark: lighten(buttonBackground, 0.2), light: darken(buttonBackground, 0.2), hcDark: null, hcLight: null }, nls.localize('buttonHoverBackground', "Button background color when hovering."));
 export const buttonBorder = registerColor('button.border', { dark: contrastBorder, light: contrastBorder, hcDark: contrastBorder, hcLight: contrastBorder }, nls.localize('buttonBorder', "Button border color."));