How to edit default dark theme for Visual Studio Code?

In VS code 'User Settings', you can edit visible colours using the following tags(this is a sample and there are much more tags),

"workbench.colorCustomizations": {
    "list.inactiveSelectionBackground": "#C5DEF0",
    "sideBar.background": "#F8F6F6",
    "sideBar.foreground": "#000000",
    "editor.background": "#FFFFFF",
    "editor.foreground": "#000000",
    "sideBarSectionHeader.background": "#CAC9C9",
    "sideBarSectionHeader.foreground": "#000000",
    "activityBar.border": "#FFFFFF",
    "statusBar.background": "#102F97",
    "scrollbarSlider.activeBackground": "#77D4CB",
    "scrollbarSlider.hoverBackground": "#8CE6DA",
    "badge.background": "#81CA91"}

If you want to edit some C++ color tokens, use the following tag,

"editor.tokenColorCustomizations": {
    "numbers": "#2247EB",
    "comments": "#6D929C",
    "functions": "#0D7C28"
}