盒子内容水平居中对齐:text-algin: center;
盒子内容垂直居中对齐:内容行高等于盒子高度;line-height == width
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盒子水平居中对齐:margin: 0 auto; margin:auto; margin-left:auto;margin-right:auto;
盒子内容水平居中对齐:text-algin: center;
盒子内容垂直居中对齐:内容行高等于盒子高度;line-height == width
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盒子水平居中对齐:margin: 0 auto; margin:auto; margin-left:auto;margin-right:auto;