JSFiddle - React, Tailwind, and code Playground

HTML

<input id="save" type="button" value="Salvar log" />
<input id="delete" type="button" value="Excluir log" />

<form id="form">
	<label>Deadline:</label>	<input type="date" id="deadline">
  <br />
  <input id="create" type="button" value="Create" />
</form>

<form>
	<label>Hoje: <span id="hoje"></span></label>
  <br />
  <input id="avancar" type="button" value="Avançar dia" />
</form>

<div id="result"></div>

CSS

form {
  margin: 5% 0%;
}

JavaScript

$(function(){
  var today = new Date(new Date().toDateString());	// salva o dia de hoje
  $('#hoje').html(today);	// exibe o dia de hoje na tela
    
  var deadline = new Date(localStorage.getItem('deadline'));	// recupera o valor já salvo no localstorage com o deadline
  
	function diff(deadline) {
    var diffTime = deadline.getTime() - today.getTime();
    var diffDays = Math.ceil(diffTime / (1000 * 60 * 60 * 24));
    return diffDays;
  }
  
  function showDiff(date) {
    $('#result').prepend("<div>" + date + "</div>");
  }
  
  if (deadline) {
  	var date = new Date(deadline);
    showDiff(diff(date));
  }
  
  $('#save').click(function () {
  	localStorage.setItem("log", $("#result").html())
  });
  
  $('#delete').click(function () {
  	localStorage.removeItem("log")
  });
  
  $('#create').click(function () {
  	$('#result').html("")
    deadline = new Date($('#deadline').val());
    deadline.setMinutes(deadline.getMinutes() + deadline.getTimezoneOffset());
    showDiff(diff(deadline));
    localStorage.setItem('deadline', deadline);
  });
  
  $('#avancar').click(function () {
  	today.setMinutes(1440)
  	$('#hoje').html(today)
    showDiff(diff(deadline));
  });
});