How to access object properties before inizialization in JavaScript/ Typescript?

I need to create a “Themes” object, which should contain all the themes with the colors I need for an app. I would like to use some of its variables to change its others. For example, having the “disabled” property set to the text color of the object + some opacity.
I tried to achieve this by using this.variableName in template literals strings but I get an error saying I can’t access it before initialization.
Is there any way to achieve this without having to copy-paste the text each time manually?

Code sample:

const Themes = {
    Dark: {
        isDark: true,
        BackgroundColors: {
          primary: '#622BFF',
          page: '#080246',
          floating: '#1C1A70',
          error: '#FF004F',
          warning: '#FCE35E',
          success: '#2ACF58',
          // I thought adding ${this.variableName} would have worked but unfortunately it doesn't
          menu: `linear-gradient(180deg, ${this.Dark.BackgroundColors.floating} 0%, 
                 rgba(242, 24, 155, 0.9) 12%,  ${this.Dark.BackgroundColors.floating} 100%)`,
          
        },
        ContentColors: {
          shared: '#622BFF',
          text: '#FFFFFF',
          //adding 99 for opacity
          disabled: `${this.Dark.ContentColors.text}99`,
          inverted: '${this.Dark.BackgroundColors.page}',
        },
      },
      Light:{
          ......
      }
}