.wrapper
  .header
    .inner
      ul.btns
        li.btn.a Button
        li.btn.b Button
        li.btn.c Button
  .body
    h1.ttl MIN-WIDTH: 980px

* {
  user-select: none;
}

.wrapper {
  min-width: 980px;
  min-height: 200vh;
  background: #1d1f20;
}

.header {
  $height: 70px;

  position: relative;
  width: 100%; height: $height;
  
  .inner {
    box-sizing: border-box;
    position: fixed;
    border-bottom: 5px solid #343436;
    min-width: 980px;
    width: 100%; height: $height;
    background: linear-gradient(#080808, #000000);
    box-shadow: 0 1px 1px black;
    z-index: 10;
  }
}

.btns {
  float: right;
  padding: 3.5px;
  overflow: hidden;
  
  .btn {
    box-sizing: border-box;
    float: left;
    margin: 3.5px;
    padding: 0 15px;
    border: solid 3px #343436;
    border-radius: 2px;
    height: 50px;
    color: #fff;
    font: 15px "Lato", "Lucida Grande","Lucida Sans Unicode", Tahoma, Sans-Serif;
    line-height: 43px;
    cursor: pointer;
  
    &:before {
      margin: 0 10px 0 0;
      color: transparent;
      font: 15px AvenirNext-Heavy;
      -webkit-text-stroke: 1px #fff;
    }
    
    &.a {
      &:before {
        content: "A";
      }
    }
    
    &.b {
      &:before {
        content: "B";
      }
    }
    
    &.c {
      &:before {
        content: "C";
      }
    }
    
    &:hover {
      background: #4d4d50;  
    }
  }
}

.ttl {
  position: absolute;
  top: 0; bottom: 0;
  left: 0; right: 0;
  margin: auto;
  width: 980px; height: 40px;
  color: #4d4d50;
  font: 30px AvenirNext-Heavy;
  text-align: center;
  line-height: 40px;
}

class Header {
  constructor(selector) {
    const _handleScroll = () => {
      this.setLeft(-window.scrollX);
    };

    this.elm = document.querySelector(selector);

    window.addEventListener('scroll', _handleScroll);
  }

  setLeft(left) {
    this.elm.style.left = `${left}px`;
  }
}

new Header('.header');