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HTML 

              
                <div class="wrapper">
  <h1></h1>
  <h2>text-align:center;</h2>
  <div class="demo-01">
    <div class="outer">
      <div class="inner">
        Lorem ipsum dolor sit amet, consectetur adipiscing elit,<br>sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
      </div>
    </div>
  </div>
  <h2>margin:0 auto;</h2>
  <div class="demo-02">
    <div class="outer">
      <div class="inner">
        Lorem ipsum dolor sit amet, consectetur adipiscing elit,<br>sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
      </div>
    </div>
  </div>
  <h2>display:inline-block;</h2>
  <div class="demo-03">
    <div class="outer">
      <div class="inner">
        Lorem ipsum dolor sit amet, consectetur adipiscing elit,<br>sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
      </div>
    </div>
  </div>
  <h2>vertical-align:middle;</h2>
  <div class="demo-04">
    <div class="outer">
      <div class="inner">
        Lorem ipsum dolor sit amet, consectetur adipiscing elit,<br>sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
      </div>
    </div>
  </div>
  <div class="demo-04 sample">
    <h3>【使用例】</h3>
    <div class="table">
      <div class="cells point">
        <p>POINT</p>
      </div>
      <div class="cells">
        <p class="title">vertical-align: middle;</p>
        <p>内容量よりも高さのあるブロックにおいて、中身を上下中央寄せにしたいときはvertical-alignの出番です。</p>
      </div>
    </div>
  </div>
  <h2>position:absolute; + margin: auto;</h2>
  <div class="demo-05">
    <div class="outer">
      <div class="inner">
        Lorem ipsum dolor sit amet, consectetur adipiscing elit,<br>sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
      </div>
    </div>
  </div>
  <h2>transform</h2>
  <div class="demo-06">
    <div class="outer">
      <div class="inner">
        Lorem ipsum dolor sit amet, consectetur adipiscing elit,<br>sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
      </div>
    </div>
  </div>
  <div class="demo-06 sample">
    <h3>【ネガティブマージンの使用例】</h3>
    <a href="#" class="btn">
      ボタン<i class="c-ico-arrow-right"></i>
    </a>
    <a href="#" class="btn">
      文字量が<br>多めのボタン<i class="c-ico-arrow-right"></i>
    </a>
    <a href="#" class="btn">
      文字量が<br>とてもとても<br>多めのボタン<i class="c-ico-arrow-right"></i>
    </a>
  </div>
  <h2>display:flex;</h2>
  <div class="demo-07">
    <div class="outer">
      <div class="inner">
        Lorem ipsum dolor sit amet, consectetur adipiscing elit,<br>sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
      </div>
    </div>
  </div>
</div>
!

CSS 

              
                /* base
----------------------------------------------------*/
*{
  -webkit-box-sizing: border-box;
  box-sizing: border-box;
}
html {
  font-size: 87.5%;
  font-family: "Roboto","ヒラギノ角ゴ Pro W3", "Hiragino Kaku Gothic Pro", Osaka, "メイリオ", Meiryo, "ＭＳ Ｐゴシック", "MS PGothic", sans-serif;
  line-height: 1.6;
  letter-spacing: .05em;
}
body {
  font-size: 14px;
  font-size: 1rem;
}
h2{
  font-weight:normal;
}
h3{
  font-weight:normal;
  margin-top: 0;
}
.wrapper{
  width: 80%;
  margin: 0 auto;
  max-width: 712px;
  min-width: 350px;
}
div[class^=demo]{
  margin-bottom: 5rem;
}
.sample{
  border-left: 3px solid #ddd;
  padding: 10px 0 10px 20px;
  margin-left: 10px;
}
/* common
----------------------------------------------------*/
.outer{
padding: 10px;
background: #e6ecf2;
}
.demo-04 .outer,
.demo-05 .outer,
.demo-06 .outer,
.demo-07 .outer{
    height: 10rem;
    text-align: center;
}
.inner{
background: rgba(255,255,255,0.3);
border: 1px solid #fff;
}

/* 【1】text-align: center;
----------------------------------------------------*/
.demo-01 .inner{
  text-align: center;
}
/* 【2】margin: 0 auto;
----------------------------------------------------*/
.demo-02 .inner{
  width: 80%;
  margin: 0 auto;
  max-width: 500px;
}
/* 【3】display: inline-block;
----------------------------------------------------*/
.demo-03 .outer{
  text-align: center;
}
.demo-03 .inner{
  display: inline-block;
  text-align: left;
}
/* 【4】vertical-align: middle;
----------------------------------------------------*/
.demo-04 .outer{
  display: table;
  width: 100%;
}
.demo-04 .inner{
  display: table-cell;
  vertical-align: middle;
}
/*使用例*/
.demo-04 .table{
  color: #706f6f;
  display: table;
  width:60%;
  border: 1px solid #d5d5d5;
}
.demo-04 .cells{
  display: table-cell;
  padding:.5rem 1rem;
}
.demo-04 .point{
   background: #f58f85;
  color: #fff;
  width:30%;
  text-align:center;
  vertical-align:middle;
  font-weight: bold;
}
.demo-04 .title{
  color :#b40000;
  font-weight: bold;
}
/* 【5】position: absolute; + margin: auto;
----------------------------------------------------*/
.demo-05 .outer{
  position: relative;
}
.demo-05 .inner{
  width: 80%;
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  height: 3.2rem;
  margin: auto;
}
/* 【6】transform
----------------------------------------------------*/
.demo-06 .outer{
  position: relative;
}
.demo-06 .inner{
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translateY(-50%) translateX(-50%);
  -webkit- transform: translateY(-50%) translateX(-50%);
}
/*ネガティブマージンの使用例*/
.demo-06 .btn{
  background: #2e6fcf;
  text-decoration: none;
  text-align: left;
  color:#fff;
  width: 30%;
  margin-right:2%;
  padding: .5em 1.5em .5em 2em;
  position: relative;
  display: inline-block;
  vertical-align: middle;
}
.demo-06 .btn i{
    margin-top: -.5em;
    position: absolute;
    right: 1em;
    top: 50%;
    line-height: 1;
}
.demo-06 .btn i:before{
  content:"＞";
  font-style: normal;
  font-weight: bold;
}

/* 【7】display: flex;
----------------------------------------------------*/
.demo-07 .outer{
	display: flex;
	justify-content: center;
	align-items: center;
}
!

JS
!
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