Summarize the solutions to the css centering problem

Problems encountered in CSS centeringSummary

Horizontal centering

• [Inline elements] Applicable to inline, inline-block, inline-table , inline-flex element

  .center {
    text-align: center;
  }

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• [Block-level element] applies to block level elements

  ①One block-level element

     .center {
   margin: 0 auto;
     }

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  ②Multiple blocks Level element

  方法一：将块级元素变为行内块级元素
  
  html部分：
  <main class="inline-block-center">
    <p>1</p>
    <p>2</p>
    <p>3</p>
  </main>
  css部分：
  .inline-block-center {
    text-align: center;
  }
  .inline-block-center p {
    display: inline-block;
    text-align: left;
  }
  
  
  方法二：flex布局
  
  html部分：
  <main class="flex-center">
    <p>1</p>
    <p>2</p>
    <p>3</p>
  </main>
  css部分：
  .flex-center{
      display:flex;
    justify-content:center;
  }

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Vertically centered

• [Inline element]

  ①Single inline element:

  Case 1: When the link or text has wrapped elements, set equal upper and lower padding

  .link {
    padding-top: 30px;
    padding-bottom: 30px;
  }

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  Case 2: When the link or text is not wrapped, set the line height and height to be equal

  .center-text-trick {
    height: 100px;
    line-height: 100px
  }

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  ②Multiple Inline elements:

  方法一：将多个行内元素分别置于table-cell中
  
  html部分:
  <table>
    <tr>
  <td>
    1
  </td>
    </tr>
  </table>
  css部分：
  table td {
    background: black;
    color: white;
    padding: 20px;
    border: 10px solid white;
    /* default is vertical-align: middle; */
  }
  
  
  方法二：将父元素设置为display:table,将自身设置为display:table-cell
  
  html部分：
  <p class="center-table">
    <p>1</p>
  </p>
  css部分：
  .center-table {
    display: table;
    height: 250px;
    width: 240px;
  }
  .center-table p {
    display: table-cell;
    vertical-align: middle;
  }
  
  
  方法三：使用felex
  
  html部分：
  <p class="flex-center">
    <p>1</p>
  </p>
  css部分：
  .flex-center{
    display: flex;
    justify-content: center;
    flex-direction: column;
    height: 400px;/*父容器必须有固定高度*/
  }
  
  
  方法四：当以上代码均不可用时，可尝试此奇淫巧技
  
  html部分：
  <p class="ghost-center">
    <p>1</p>
  </p>
  css部分：
  .ghost-center {
    position: relative;
  }
  .ghost-center::before {
    content: " ";
    display: inline-block;
    height: 100%;
    width: 1%;
    vertical-align: middle;
  }
  .ghost-center p {
    display: inline-block;
    vertical-align: middle;
  }

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• [Block-level elements]

  ①Known element height (absolute positioning+negative margin)

  .parent {
    position: relative;
  }
  .child {
    position: absolute;
    top: 50%;
    height: 100px;
    margin-top: -50px; /* 为元素高度的一半，没有box-sizing时，为height+padding+border的一半*/
  }

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  ②I don’t know the height of the element (similar to the previous method)

  .parent {
    position: relative;
  }
  .child {
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
  }

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  ③flex layout

  .parent {
    display: flex;
    flex-direction: column;
    justify-content: center;
  }

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centered horizontally and vertically

①Yes Elements with fixed width and height

.parent {
  position: relative;
}

.child {
  width: 300px;
  height: 100px;
  padding: 20px;

  position: absolute;
  top: 50%;
  left: 50%;

  margin: -70px 0 0 -170px;/* 注意此处为height+padding+的一半*/
}

②Elements without fixed width and height (same as the previous elements without fixed width and height, use transform to solve)

.parent {
  position: relative;
}
.child {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

③Use flexbox layout

.parent {
  display: flex;
  justify-content: center;
  align-items: center;
}

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