CreateTheme

First, create a JSON file, name it as follows: the-name-of-the-theme.json. The themes use defined color/elements keys.
All colors must be enter in hexadecimal, rgb or rgba!

Then create three dictionaries in your JSON named terminal, app and theme in terminal key, like that:

{
    "terminal": {
        "theme": {}
    },
    "app": {}
}

Theme keys

foreground: The terminal foreground color.
background: The terminal background color.
black: The shade of black used.
blue: The shade of blue used.
cyan: The shade of cyan used.
green: The shade of green used.
magenta: The shade of magenta used.
red: The shade of red used.
White: The shade of White used.
yellow: The shade of yellow used.
brightBlack: The shade of bright black used.
brightBlue: The shade of bright blue used.
brightCyan: The shade of bright cyan used.
brightGreen: The shade of bright green used.
brightMagenta: The shade of bright magenta used.
brightRed: The shade of bright red used.
brightWhite: The shade of bright white used.
brightYellow: The shade of bright yellow used.

App keys

textColor: The default text color.
tabActive: The active tab color.
tabInactive: The inactive tab color.
topBar: The top bar color.
background: The settings background color.
secondaryBackground: The secondary settings background color.
backgroundHover: The background app hover color.
buttonRadius: The button radius percentage.
appBackground: The background of all panels except the terminals.