CSS居中布局方案

水平居中

/* solution1 */
.parent {
  text-align: center;
}
.child {
  display: inline-block;
}

/* soluction2 */
.child {
  display: table;
  margin: 0 auto;
}

/* solution3 */
.parent {
  position: relative;
}
.child {
  position: absolute;
  left: 50%;
  transform: translateX(-50%);
}

/* solution4 */
.parent {
  display: flex;
  justify-content: center;
}

垂直居中

/* solution1 */
.parent {
  display: table-cell;
  vertical-align: middle;    
}

/* solution2 */
.parent {
  position: relative;
}
.child { 
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
}

/* solution3 */
.parent {
  display: flex;
  align-items: center;
}

/* solution4 */
.parent {
  height: 300px;
  writing-mode: vertical-lr;
}
.child {
  height: 100px;
  margin: auto;
}

水平垂直居中

/* solution1 */
.parent {
  display: table-cell;
  text-align: center;
  vertical-align: middle;
}
.child {
  display: inline-block;
}

/* solution2 */
.parent {
  position: relative;     
}
.child {
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
}

/* solution3 */
.parent {
  display: flex;
  justify-content: center;
  align-items: center;   
}

/* solution4 */
.parent {
  width: 300px;
  height: 150px;
  position: relative;
}
.child {
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  width: 50px;
  height: 50px;
  margin: auto;
}