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内容组成####
/**
* CONTENTS
*
* SETTINGS
* Global...............Globally-available variables and config.
*
* TOOLS
* Mixins...............Useful mixins.
*
* GENERIC
* Normalize.css........A level playing field.
* Box-sizing...........Better default `box-sizing`.
*
* BASE
* Headings.............H1–H6 styles.
*
* OBJECTS
* Wrappers.............Wrapping and constraining elements.
*
* COMPONENTS
* Page-head............The main page header.
* Page-foot............The main page footer.
* Buttons..............Button elements.
*
* TRUMPS
* Text.................Text helpers.
*/
