看看下面的CSS在Windows 8 metro风格的应用程序，什么是“fr”？
-ms-grid-columns: 638px 1fr;
解决方法
它代表“分数”或“分数单位”，在CSS级别3中提出的单位。
从https://www.w3.org/TR/css3-grid-layout/#fr-unit：
Fraction values are new units applicable to the grid-rows and grid-columns properties…
The distribution of fractional space occurs after all or content-based row and column sizes have reached their maximum. The total size of the rows or columns is then subtracted from the available space and the remainder is divided proportionately among the fractional rows and columns.
从http://msdn.microsoft.com/en-us/library/windows/apps/hh780610.aspx：
…fractional unit (1FR)… represents one share of all the space available to the grid after fixed-size and auto-sized tracks (rows or columns) are laid out.
1fr is one “fractional unit”,which is a way of saying “the remaining space in the element”.
