Implement the jQuery single-character function $ which only needs to supports the css() method that either gets the value of a computed style property or sets a CSS property on the matched element.

app.tsx

import $ from './functions/jQuery.css';
document.body.innerHTML = '<button>Click me</button>';
$('button')
  .css('color', 'red')
  .css('backgroundColor', 'tomato')
  .css('fontSize', '16px');
$('button').css('color'); 

jQuery.css.ts

interface JQuery {
  css: (
    prop: string,
    value?: boolean | string | number
  ) => JQuery | string | undefined;
}

export default function $(selector: string): JQuery {
  const element = document.querySelector(selector) as HTMLElement;

  return {
    css: function (prop: string, value?: boolean | string | number) {
      if (value) {
        if (element) (element?.style as any)[prop] = value;
        return this;
      } else {
        const styleValue = element ? (element?.style as any)[prop] : '';
        return styleValue.length > 0 ? styleValue : undefined;
      }
    },
  };
}