Here a short and concise answer with an example.
You will have to edit settings.json.
To do that click: file->preferences->settings->workbench->color customizations (or simply search for 'color customization' in settings).
Within this json you will find "editor.tokenColorCustomizations" and "workbench.colorCustomizations". These nested JSONs are what you are looking for.
To understand how to customize every single token have a look to the amazing answer of Joey in this similar question.
But if you are lazy (like me) and does not want to read a lot, here a practical example. Just paste these two elements in the root json of settings.json to override the Dark theme. I commented the most important parts. Enjoy
"workbench.colorCustomizations": {
"[*Dark*]": { // terminal colors
"terminal.background": "#181818",
"terminal.foreground": "#00ff00",
"terminalCursor.background": "#D8D8D8",
"terminalCursor.foreground": "#D8D8D8",
"terminal.ansiBlack": "#181818",
"terminal.ansiBlue": "#7CAFC2",
"terminal.ansiBrightBlack": "#585858",
"terminal.ansiBrightBlue": "#7CAFC2",
"terminal.ansiBrightCyan": "#86C1B9",
"terminal.ansiBrightGreen": "#A1B56C",
"terminal.ansiBrightMagenta": "#BA8BAF",
"terminal.ansiBrightRed": "#AB4642",
"terminal.ansiBrightWhite": "#F8F8F8",
"terminal.ansiBrightYellow": "#F7CA88",
"terminal.ansiCyan": "#86C1B9",
"terminal.ansiGreen": "#A1B56C",
"terminal.ansiMagenta": "#BA8BAF",
"terminal.ansiRed": "#AB4642",
"terminal.ansiWhite": "#D8D8D8",
"terminal.ansiYellow": "#F7CA88",
// background
"editor.background": "#0f0f0f",
// brackets
"editorBracketHighlight.foreground1": "#FAE734",
"editorBracketHighlight.foreground2": "#DE6257",
"editorBracketHighlight.foreground3": "#F58A6B",
"editorBracketHighlight.foreground4": "#DE8657",
"editorBracketHighlight.foreground5": "#FAA75A",
"editorBracketHighlight.foreground6": "#abb2c0",
// various errors
"editorBracketHighlight.unexpectedBracket.foreground": "#ff0008",
"editor.rangeHighlightBackground": "#ff0008",
}
},
// custom
"editor.tokenColorCustomizations": {
"[*Dark*]": {
"strings": "#4AFF43",
"numbers": "#1cdfdf",
"functions": "#a856ff",
"variables": "#F5AB76",
"comments": "#1ABEE8",
"textMateRules": [
{
// function parameters
"scope": "variable.parameter",
"settings": {
"fontStyle": "",
"foreground": "#F5762A"
}
},
{
// language constants such as bools
"scope": "constant.language",
"settings": {
"fontStyle": "",
"foreground": "#FF299E"
}
}
]
}
},
"editor.semanticTokenColorCustomizations": {
"enabled": true,
},