line-height 属性设置行间的距离（行高）。
该属性会影响行框的布局。在应用到一个块级元素时，它定义了该元素中基线之间的最小距离而不是最大距离。
line-height 与 font-size 的计算值之差（在 CSS 中成为“行间距”）分为两半，分别加到一个文本行内容的顶部和底部。可以包含这些内容的最小框就是行框。
总结：line-height减去font-size，所得的高是当前文字的顶端距离上一行文字的底端的长度。或者说是line-height包含了font-size，而其差值则平分在font-size即文字的上下两侧了！
其中line-height似乎不能为负的样子，但它与font-size的差值可以为负，如果为负的话，二行文本就会出现重叠现象了！
需要注意的是line-height可以填相对值，如1，表示与font-size同。
本文仅仅作个记录，若要详细了解请自行网上搜索或见参考资料。
参考资料：
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