Tailwind css border color not working on web page

I am just trying with tailwindcss, I got stuck at very basic thing. I tried different tailwindcss's utility classed and it worked. But now I am stuck at border-color

<div className="px-4 border-gray-900 border-solid">
   <a href="#" className="block font-semibold">Menu1</a>
   <a href="#" className="block ">Menu2</a>
   <a href="#" className="block ">Menu3</a>
   <a href="#" className="block ">Login</a>
</div>

I can inspect the elements and it is crossed in inspect element which means somehow it is not being applied to dom.

module.exports = {
  purge: [],
  theme: {
    extend: {
      colors: {
        primary: 'var(--color-primary)',
        secondary: 'var(--color-secondary)',
        negative: 'var(--color-negative)',
        positive: 'var(--color-positive)',
        'primary-background': 'var(--background-primary)',
        'sec-background': 'var(--background-sec)',
        'primary-text': 'var(--color-text-primary)',
      },
    },
    backgroundColor: (theme) => ({
      ...theme('colors'),
    }),
    borderColor: (theme) => ({
      ...theme('colors'),
    }),
  },
  variants: {
    backgroundColor: ['active'],
    borderStyle: ['responsive'],
  },
  plugins: [],
};

This is how my tailwind.config.js looks like

Attaching an image