<div class="box" style=" margin: 0px !important; padding: 0px !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border-bottom-right-radius: 0px !important; border-bottom-left-radius: 0px !important; border: 0px !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; line-height: 1.8em !important; outline: 0px !important; overflow: visible !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; width: auto !important; box-sizing: content-box !important; font-family: Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace !important; min-height: inherit !important; background: none !important;">>

    fdasjfdlas

</div>

五、ex 和 ch

ex、ch单位与em、rem相似之处在于都依赖于font-size，但是ex、ch还依赖于font-family，基于font-specific来计算。 引用w3C规范：

ex unit Equal to the used x-height of the .  The x-height is so called because it is often equal to the height of the lowercase "x". However, an ‘’ is defined even for fonts that do not contain an "x". The x-height of a font can be found in different ways. Some fonts contain reliable metrics for the x-height. If reliable font metrics are not available, UAs may determine the x-height from the height of a lowercase glyph. One possible heuristic is to look at how far the glyph for the lowercase "o" extends below the baseline, and subtract that value from the top of its bounding box. In the cases where it is impossible or impractical to determine the x-height, a value of 0.5em must be assumed. ch unit Equal to the used advance measure of the "0" (ZERO, U+0030) glyph found in the font used to render it.  

用一副图来解释这两种单位的含义：

这两种单位，有许多用途，大部分是用于印刷时的微调整。例如，sup、sub元素分别显示上标和下标，但是我们可以使用position和bottom模拟：

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<style type="text/css">

body {

    margin: 0;

    padding:0;

}

 

.sup {

    position: relative;

    bottom: 1ex;

}

.sub {

    position: relative;

    bottom: -1ex;

}

</style>

<div>

    AaB<span class="sup">b</span>CcXxD<span class="sub">d</span>EeFf

</div>