index.html

<div class="wrapper">
  <header class="header">
    <div class="header__container">
      <a href="" class="header__logo"></a>
      <div class="header__menu menu">
        <div class="menu__icon">
          <span></span>
        </div>
        <nav class="menu__body">
          <ul class="menu__list">
            <li><a data-goto=".page__section_1" href="#" class="menu__link">Раздел №1</a></li>
            <li><a data-goto=".page__section_2" href="#" class="menu__link">Раздел №2</a></li>
            <li><a data-goto=".page__section_3" href="#" class="menu__link">Раздел №3</a></li>
            <li>
              <a href="" class="menu__link">Страница №1</a>
              <span class="menu__arrow"></span>
              <ul class="menu__sub-list">
                <li>
                  <a href="" class="menu__sub-link">Раздел страницы №1</a>
                </li>
                <li>
                  <a href="" class="menu__sub-link">Раздел страницы №2</a>
                </li>
                <li>
                  <a href="" class="menu__sub-link">Раздел страницы №3</a>
                </li>
              </ul>
            </li>
            <li>
              <a href="" class="menu__link">Страница №2</a>
            </li>
          </ul>
        </nav>
      </div>
    </div>
  </header>
  <main class="page">
    <section class="page__section page__section_1">
      <h1 class="page__title">Отличная статья</h1>
      <div class="page__text">
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
      </div>
    </section>
    <section class="page__section page__section_2">
      <h2 class="page__sub-title">Отличный раздел сайта</h2>
      <div class="page__text">
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
      </div>
    </section>
    <section class="page__section page__section_3">
      <h2 class="page__sub-title">Отличный раздел сайта</h2>
      <div class="page__text">
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
        <p>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Doloribus neque ratione modi mollitia natus
          voluptas culpa architecto officiis, sed dolorem quasi? Voluptatem laborum ad assumenda quos officiis provident
          quaerat libero.</p>
      </div>
    </section>
  </main>
</div>

script.js

"use strict"

const isMobile = {
	Android: function () {
		return navigator.userAgent.match(/Android/i);
	},
	BlackBerry: function () {
		return navigator.userAgent.match(/BlackBerry/i);
	},
	iOS: function () {
		return navigator.userAgent.match(/iPhone|iPad|iPod/i);
	},
	Opera: function () {
		return navigator.userAgent.match(/Opera Mini/i);
	},
	Windows: function () {
		return navigator.userAgent.match(/IEMobile/i);
	},
	any: function () {
		return (
			isMobile.Android() ||
			isMobile.BlackBerry() ||
			isMobile.iOS() ||
			isMobile.Opera() ||
			isMobile.Windows());
	}
};

if (isMobile.any()) {
	document.body.classList.add('_touch');

	let menuArrows = document.querySelectorAll('.menu__arrow');
	if (menuArrows.length > 0) {
		for (let index = 0; index < menuArrows.length; index++) {
			const menuArrow = menuArrows[index];
			menuArrow.addEventListener("click", function (e) {
				menuArrow.parentElement.classList.toggle('_active');
			});
		}
	}

} else {
	document.body.classList.add('_pc');
}

// Меню бургер
const iconMenu = document.querySelector('.menu__icon');
const menuBody = document.querySelector('.menu__body');
if (iconMenu) {
	iconMenu.addEventListener("click", function (e) {
		document.body.classList.toggle('_lock');
		iconMenu.classList.toggle('_active');
		menuBody.classList.toggle('_active');
	});
}


// Прокрутка при клике
const menuLinks = document.querySelectorAll('.menu__link[data-goto]');
if (menuLinks.length > 0) {
	menuLinks.forEach(menuLink => {
		menuLink.addEventListener("click", onMenuLinkClick);
	});

	function onMenuLinkClick(e) {
		const menuLink = e.target;
		if (menuLink.dataset.goto && document.querySelector(menuLink.dataset.goto)) {
			const gotoBlock = document.querySelector(menuLink.dataset.goto);
			const gotoBlockValue = gotoBlock.getBoundingClientRect().top + pageYOffset - document.querySelector('header').offsetHeight;

			if (iconMenu.classList.contains('_active')) {
				document.body.classList.remove('_lock');
				iconMenu.classList.remove('_active');
				menuBody.classList.remove('_active');
			}

			window.scrollTo({
				top: gotoBlockValue,
				behavior: "smooth"
			});
			e.preventDefault();
		}
	}
}

style.css

.page {
  padding: 90px 0px 30px 0px;
}

.page__section {
  padding: 30px;
  max-width: 1200px;
  margin: 0px auto;
}

.page__section_1 {
  background-color: #794f45;
}

.page__section_2 {
  background-color: #77608d;
}

.page__section_3 {
  background-color: #7a956b;
}

.page__title {
  font-size: 40px;
  margin: 0px 0px 20px 0px;
}

.page__text {
  font-size: 16px;
  line-height: 150%;
}

.page__text p {
  margin: 0px 0px 20px 0px;
}

.page__sub-title {
  font-size: 30px;
  margin: 0px 0px 20px 0px;
}

.header {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  z-index: 10;
  background-color: #912105;
}

.header__container {
  max-width: 1200px;
  margin: 0px auto;
  display: flex;
  padding: 0px 30px;
  align-items: center;
  justify-content: space-between;
  min-height: 70px;
}

.header__logo {
  border-radius: 50%;
  background-color: #fff;
  position: relative;
  z-index: 5;
  width: 40px;
  height: 40px;
}

.header__menu {}

.menu {}

.menu__icon {
  display: none;
}

.menu__body {}

.menu__list {}

.menu__list>li {
  position: relative;
  margin: 0px 0px 0px 20px;
}

.menu__link {
  color: #fff;
  font-size: 18px;
}

.menu__link:hover {
  text-decoration: underline;
}

.menu__sub-list {
  position: absolute;
  top: 100%;
  right: 0;
  background-color: #000;
  padding: 15px;
  min-width: 200px;
}

.menu__sub-list li {
  margin: 0px 0px 10px 0px;
}

.menu__sub-list li:last-child {
  margin: 0;
}

.menu__sub-link {
  color: #fff;
}

.menu__sub-link:hover {
  text-decoration: underline;
}

.menu__arrow {
  display: none;
}

/* ----------------------- */
body._pc .menu__list>li:hover .menu__sub-list {
  opacity: 1;
  visibility: visible;
  transform: translate(0px, 0px);
  pointer-events: all;
}

body._touch .menu__list>li {
  display: flex;
  align-items: center;
}

body._touch .menu__link {
  flex: 1 1 auto;
}

body._touch .menu__arrow {
  display: block;
  width: 0;
  height: 0;
  margin: 0px 0px 0px 5px;
  transition: transform 0.3s ease 0s;
  border-left: 5px solid transparent;
  border-right: 5px solid transparent;
  border-top: 10px solid #fff;
}

body._touch .menu__list>li._active .menu__sub-list {
  opacity: 1;
  visibility: visible;
  transform: translate(0px, 0px);
  pointer-events: all;
}

body._touch .menu__list>li._active .menu__arrow {
  transform: rotate(-180deg);
}

/* ----------------------- */
@media (min-width: 767px) {
  .menu__list {
    display: flex;
    align-items: center;
  }

  .menu__list>li {
    padding: 10px 0;
  }

  .menu__sub-list {
    transform: translate(0px, 10%);
    opacity: 0;
    visibility: hidden;
    pointer-events: none;
    transition: all 0.3s ease 0s;
  }
}

@media (max-width: 767px) {
  .menu__icon {
    z-index: 5;
    display: block;
    position: relative;
    width: 30px;
    height: 18px;
    cursor: pointer;
  }

  .menu__icon span,
  .menu__icon::before,
  .menu__icon::after {
    left: 0;
    position: absolute;
    height: 10%;
    width: 100%;
    transition: all 0.3s ease 0s;
    background-color: #fff;
  }

  .menu__icon::before,
  .menu__icon::after {
    content: "";
  }

  .menu__icon::before {
    top: 0;
  }

  .menu__icon::after {
    bottom: 0;
  }

  .menu__icon span {
    top: 50%;
    transform: scale(1) translate(0px, -50%);
  }

  .menu__icon._active span {
    transform: scale(0) translate(0px, -50%);
  }

  .menu__icon._active::before {
    top: 50%;
    transform: rotate(-45deg) translate(0px, -50%);
  }

  .menu__icon._active::after {
    bottom: 50%;
    transform: rotate(45deg) translate(0px, 50%);
  }

  .menu__body {
    position: fixed;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.9);
    padding: 100px 30px 30px 30px;
    transition: left 0.3s ease 0s;
    overflow: auto;
  }

  .menu__body._active {
    left: 0;
  }

  .menu__body::before {
    content: "";
    position: fixed;
    width: 100%;
    top: 0;
    left: 0;
    height: 70px;
    background-color: #912105;
    z-index: 2;
  }

  .menu__list>li {
    flex-wrap: wrap;
    margin: 0px 0px 30px 0px;
  }

  .menu__list>li:last-child {
    margin-bottom: 0;
  }

  .menu__list>li._active .menu__sub-list {
    display: block;
  }

  .menu__link {
    font-size: 24px;
  }

  .menu__sub-list {
    position: relative;
    background-color: #fff;
    flex: 1 1 100%;
    margin: 20px 0px 0px 0px;
    display: none;
  }

  .menu__sub-link {
    font-size: 20px;
    color: #000;
  }
}