JSFiddle - React, Tailwind, and code Playground

HTML

<section>
   <!--- Celsius, Fahrenheit, Kelvin  -->
   <table>
     <tr>
       <td>&#176C</td>
       <td>&#176F</td>
       <td>&#176K</td>
     </tr>
     <tr>
       <td> <input type="number" id="celsius"/> </td>
       <td id="fahr1"></td>
       <td id="kelv1"></td>
     </tr>
     <tr>
       <td id="celc2">-</td>
       <td> <input type="number" id="fahrenheit" /> </td>
       <td id="kelv2">-</td>
     </tr>
   </table>
 </section>

JavaScript

const celsius = document.getElementById('celsius');
const fahrenheit = document.getElementById('fahrenheit');

celsius.addEventListener('change', (event) => {
  convertFromCelsius();
});

fahrenheit.addEventListener('change', (event) => {
  convertFromFahrenheit();
});

function convertFromCelsius() {
	var fahr1 = document.getElementById("fahr1");
  var kelv1 = document.getElementById("kelv1");
  fahr1.textContent = parseInt(celsius.value) * (9/5) + 32;
  kelv1.textContent = parseInt(celsius.value) + 273.15;
}

function convertFromFahrenheit() {
	var celc2 = document.getElementById("celc2");
  var kelv2 = document.getElementById("kelv2");
  celc2.textContent = (parseInt(fahrenheit.value) - 32) * (5/9);
  kelv2.textContent = (parseInt(fahrenheit.value) +  459.67) * (5/9);
}