index.html

<!DOCTYPE html>
<html>
<head>
  <title>Portfolio</title>
  <meta charset="utf-8">
  <link rel="stylesheet" href="css/styles.css">
  <link href="https://fonts.googleapis.com/earlyaccess/notosanskr.css" rel="stylesheet">
</head>
<body>
  <!-- navigation bar -->
  <div class="navbar">
    <img src="images/profile_img.png" width="34" height="34">
    <ul class="menu-right">
      <li><button id="about-btn">About</button>
      <li><button id="contact-btn">Contact</button>
    </ul>
  </div>

  <section class="header">
    <div class="helper"></div><div class="vertical-center">
      <h1>I'm an engineer</h1>
      <h2>FRONT-END DEVELOPER</h2>
    </div>
  </section>

  <!-- about me -->
  <section class="about">
    <div class="helper"></div><div class="vertical-center">
      <h3>About Me</h3>
      <p>안녕하세요. 저는 프론트엔드와 백엔드를 넘나드는 개발자입니다. 만나서 반가워요!</p>

      <div class="skillset">
        <div class="skill">
          <div class="title">HTML5</div>

          <div class="bar">
            <div class="inner-bar"></div>

            <span class="percentage">90%</span>
          </div>
        </div>

        <div class="skill">
          <div class="title">CSS3</div>

          <div class="bar">
            <div class="inner-bar"></div>

            <span class="percentage">90%</span>
          </div>
        </div>

        <div class="skill">
          <div class="title">jQuery</div>

          <div class="bar">
            <div class="inner-bar"></div>

            <span class="percentage">85%</span>
          </div>
        </div>

        <div class="skill">
          <div class="title">Python</div>

          <div class="bar">
            <div class="inner-bar"></div>

            <span class="percentage">75%</span>
          </div>
        </div>

        <div class="skill">
          <div class="title">Rails</div>

          <div class="bar">
            <div class="inner-bar"></div>

            <span class="percentage">70%</span>
          </div>
        </div>

        <div class="skill">
          <div class="title">Sketch</div>

          <div class="bar">
            <div class="inner-bar"></div>

            <span class="percentage">90%</span>
          </div>
        </div>
      </div>
    </div>
  </section>

  <!-- contact me -->
  <section class="contact">
    <div class="helper"></div><div class="vertical-center">
      <h3>Contact Me</h3>
      <p>언제든지 편하게 연락주세요. 감사합니다.</p>

      <form>
        <input type="text" name="name" placeholder="NAME">
        <input type="email" name="email" placeholder="EMAIL">
        <textarea type="text" name="message" placeholder="MESSAGE"></textarea>
      </form>
    </div>
  </section>
    
  <script
    src="https://code.jquery.com/jquery-3.2.1.min.js"
    integrity="sha256-hwg4gsxgFZhOsEEamdOYGBf13FyQuiTwlAQgxVSNgt4="
    crossorigin="anonymous"></script>
  <script src="js/script.js"></script>
</body>
</html>

css/styles.css

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: 'Noto Sans KR', sans-serif;
  min-width: 768px;
}

/* navbar */

.navbar {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 60px;
  line-height: 60px;
  padding: 0 60px;
}

.navbar img {
  vertical-align: middle;
}

.navbar .menu-right {
  float: right;
  padding: 0;
  margin: 0;
  list-style: none;
}

.navbar .menu-right li {
  float: left;
}

.navbar .menu-right li button {
  color: white;
  font-size: 16px;
  font-weight: 300;
  text-decoration: none;
  transition: color 1s;
  padding: 0;
  background-color: transparent;
  border: none;
  outline: none;
  cursor: pointer;
}

.navbar .menu-right li:last-child {
  margin-left: 30px;
}

/* vertical center */

.helper {
  display: inline-block;
  height: 100%;
  vertical-align: middle;
}

.vertical-center {
  display: inline-block;
  vertical-align: middle;
  color: white;
  opacity: 0;
  position: relative;
  top: 100px;
}

/* header */

.header {
  background-image: url('../images/hero_background.jpg');
  background-size: cover;
  background-position: center center;
  height: 100vh;
  min-height: 600px;
  text-align: center;
}

.header h1 {
  font-size: 40px;
  margin: 0;
  margin-bottom: 33px;
}

.header h2 {
  font-size: 20px;
  margin: 0;
  font-weight: normal;
}

/* about */

.about {
  height: 100vh;
  min-height: 600px;
  text-align: center;
}

.about h3 {
  font-size: 40px;
  color: #4a4a4a;
  margin: 0;
  margin-bottom: 37px;
}

.about p {
  font-size: 16px;
  color: #4a4a4a;
  margin: 0;
  margin-bottom: 61px;
}

.about .skillset {
  display: inline-block;
}

.about .skill:not(:last-child) {
  margin-bottom: 17px;
}

.about .skill .title {
  display: inline-block;
  width: 50px;
  vertical-align: middle;
  margin-right: 15px;
  font-size: 16px;
  color: #4a4a4a;
}

.about .skill .bar {
  display: inline-block;
  vertical-align: middle;
  width: 646px;
  height: 33px;
  border-radius: 25px;
  background-color: #f9f9f9;
  position: relative;
  line-height: 33px;
}

.about .skill .bar .inner-bar {
  position: absolute;
  top: 0;
  left: 0;
  height: 33px;
  background: #bbe6ff;
  border-radius: 25px;
}

.about .skill .bar .percentage {
  font-size: 14px;
  color: #9b9b9b;
  position: absolute;
  right: 20px;
  top: 0;
}

/* contact */

.contact {
  height: 100vh;
  min-height: 600px;
  background-color: #f9f9f9;
  text-align: center;
}

.contact h3 {
  font-size: 40px;
  color: #4a4a4a;
  margin: 0;
  margin-bottom: 37px;
}

.contact p {
  font-size: 16px;
  color: #4a4a4a;
  margin: 0;
  margin-bottom: 61px;
}

.contact form {
  display: inline-block;
  vertical-align: middle;
  width: 646px;
}

.contact input,
.contact textarea {
  display: block;
  width: 100%;
  border-radius: 4px;
  border: solid 1px #ebebeb;
  font-size: 16px;
  padding: 10px 30px;
}

.contact input {
  margin-bottom: 24px;
}

.contact textarea {
  resize: none;
  height: 222px;
}

js/script.js

/* navbar 색 변환 , 페이지 로딩시 vertical-center 출력  */
$(document).ready(function(){
    var window_scrollTop = $(window).scrollTop();
    var about_scrollTop = $('.about').offset().top;
    var contact_scrollTop = $('.contact').offset().top;
    
    //console.log(window_scrollTop);
    //console.log(about_scrollTop);
    //console.log(contact_scrollTop);

    if(window_scrollTop < about_scrollTop){
        $('.header .vertical-center').animate({opacity : 1, top: 0}, 1000)
    }
    
});

// 변수의 반복 선언을 줋이기 위해서 해당 클래스로 가는 함수에 
// 변수를 제거하고 함수 밖에 전역변수로 정의
$(window).on('scroll', function(){    
    //window 전체 높이를 windowHeight 변수에 넣음
    var windowHeight = $(window).scrollTop();    
    //검은색 글씨로 바뀌는 부분(첫페이지 넘어서는 순간의 높이)을 blackFontHeight에 넣음
    var aboutFontHeight = $('.about').position().top;
    var contactHeight = $('.contact').position().top;  
    //console.log(windowHeight);
    //console.log(aboutFontHeight);
    //console.log(contactHeight);
    //console.log( $('.about').position().top);

    //스크롤 내릴 때, 페이지 opacity 1로 바뀌면서 서서히 나타나게 하기
    if(windowHeight <= aboutFontHeight){
        $("#about-btn, #contact-btn").css("color","#4A4A4A");            
    }else if((aboutFontHeight < windowHeight) && (windowHeight < contactHeight)){
        $('.about .vertical-center').animate({opacity : 1, top : 0}, 1000);           
    }else if(windowHeight >= contactHeight){
        $('.contact .vertical-center').animate({opacity : 1, top : 0}, 1000);    
    }

    //스크롤 내릴 때 오른쪽 위 about contact 글씨 검은색으로 바뀌게 하기
    if(windowHeight >= aboutFontHeight){
        $("#about-btn, #contact-btn").css("color","#4A4A4A");            
    }else{
        $("#about-btn, #contact-btn").css("color","#fff");            
    }  
});

// navbar의 about-btn 버튼을 클릭 하였을 때 해당위치로 가는 부분
$('#about-btn').on('click', function(){    
    var about_scrollTop = $('.about').offset().top;
    console.log(about_scrollTop);
    $('html, body').animate({scrollTop: about_scrollTop}, 1000);
});

// navbar의 contract-btn 버튼을 클릭 하였을 때 해당위치로 가는 부분
$('#contact-btn').on('click', function(){
    var contact_scrollTop = $('.contact').offset().top;
    console.log(contact_scrollTop);
    $('html, body').animate({scrollTop: contact_scrollTop}, 1000);
});

안녕하세요~

position().top 과 offset().top 의 차이가 궁금하여 구글 검색을 하던 중 궁금한 것이 있어서 질문 남깁니다.

각각 상대좌표와 절대좌표를 의미한다고 하는데요..

제가 위의 과제에서는 혼용해서 사용해보았는데, 크게 이상은 없어 보여서요..

계속 위에처럼 혼용해서 쓸지 아니면, position().top(상대좌표)으로 된 것을 offset().top(절대좌표)으로 전부 바꾸어도 괜찮은지 궁금합니다.