JSFiddle - React, Tailwind, and code Playground

HTML

<nav class="navbar">
        <div class="container">
            <div class="navbar-block">
                <div class="navbar__logo">
                    <img src="img/logo.png" alt="" srcset="">
                </div>
                <!-- /.navbar__logo -->
                <div class="navbar__info">
                    <div class="navbar__contacts">
                        <span class="navbar__address">Калуга, Москва, МО</span>
                        <a href="tel:+74954225131" class="navbar__phone">
                            +7 (495) 42-251-31
                        </a>
                    </div>
                    <!-- /.navbar__contacts -->
                    <button class="button navbar__button"  id="button">Перезвоните мне</button>
                    <!-- /.button navbar__button -->
                </div>
                <!-- /.navbar__info -->
            </div>
            <!-- /.navbar-block -->
        </div>
        <!-- /.container -->
    </nav>
    <!-- /.navbar -->
    <main>
        <section class="hero">
            <div class="container">
                <div class="hero-block">
                    <div class="hero-text">
                        <h1 class="hero-text__title">
                            Внутренняя отделка помещений "под ключ"
                        </h1>
                        <span class="hero-text__subtitle">
                            с гарантией качества, прописанной в договоре
                        </span>
                        <ul class="hero-list">
                            <li class="hero-list__item">
                                <div class="hero-list__image">
                                    <img src="img/hero/clock.png" alt="">
                                </div>
                                <span class="hero-list__text">
                                    Точно соблюдаем сроки
                                </span>
                            </li>
                            <li...

CSS

@charset "UTF-8";
@font-face {
  font-family: 'Museo Sans Light';
  src: url("../fonts/MuseoSansCyrl/MuseoSansCyrl-300.eot");
  src: url("../fonts/MuseoSansCyrl/MuseoSansCyrl-300.eot?#iefix") format("embedded-opentype"), url("../fonts/MuseoSansCyrl/MuseoSansCyrl-300.woff") format("woff"), url("../fonts/MuseoSansCyrl/MuseoSansCyrl-300.ttf") format("truetype");
  font-weight: normal;
  font-style: normal;
}

@font-face {
  font-family: 'Museo Sans Bold';
  src: url("../fonts/MuseoSansCyrl/MuseoSansCyrl-700.eot");
  src: url("../fonts/MuseoSansCyrl/MuseoSansCyrl-700.eot?#iefix") format("embedded-opentype"), url("../fonts/MuseoSansCyrl/MuseoSansCyrl-700.woff") format("woff"), url("../fonts/MuseoSansCyrl/MuseoSansCyrl-700.ttf") format("truetype");
  font-weight: normal;
  font-style: normal;
}

* {
  -webkit-box-sizing: border-box;
          box-sizing: border-box;
}

body {
  font-family: 'Museo Sans Light', sans-serif;
  font-weight: 300;
}

img {
  max-width: 100%;
}

.container {
  width: 1170px;
  margin: 0 auto;
}

@media (max-width: 1200px) {
  .container {
    width: 760px;
  }
}

@media (max-width: 768px) {
  .container {
    max-width: 580px;
    width: 95%;
  }
}

/** Общие стили для кнопок**/
.button {
  background-color: #ffd200;
  border-radius: 10px;
  border: none;
  padding: 18px 30px;
}

.section {
  padding: 90px 0;
}

.section-title {
  font-size: 24px;
  font-family: 'Museo Sans Bold', sans-serif;
  font-weight: 700;
}

.section-subtitle {
  display: block;
  font-size: 16px;
}

.input {
  border: 1px solid #dddddd;
  padding: 20px 26px;
  font-size: 15px;
  border-radius: 10px;
}

/* Стили для шапки */
.navbar {
  padding: 8px 0;
}

.navbar-block {
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-pack: justify;
      -ms-flex-pack: justify;
          justify-content: space-between;
  -webkit-box-align: center;
      -ms-flex-align: center;
          align-items: center;
}

.navbar__info {
  display: -webkit-box;
 ...

JavaScript

let button = document.querySelector("#button"),
    modal = document.querySelector("#modal"),
    close = document.querySelector("#close");
console.log(button);


button.addEventListener("click", function () {
    modal.classList.add("modal_active");
});

close.addEventListener("click", function () {
    modal.classList.remove("modal_active");
});