Mixins

Utility mixins for custom elements and responsive helpers

`=arrow($color)`	Creates a CSS-only down arrow. Used for the dropdown select.
`=block`	Defines a margin-bottom of 1.5rem, except when the element is the last child. Used for almost all block elements.
`=clearfix`	Adds a clearfix at the end of the element. Used for the "is-clearfix" helper.
`=center($size)`	Positions an element in the exact center of its parent. Used for the spinner in a loading button.
`=delete`	Creates a CSS-only cross. Used for the delete element in modals, messages, tags...
`=fa($size, $dimensions)`	Sets the style of a Font Awesome icon container.
`=hamburger($dimensions)`	Creates a CSS-only hamburger menu with 3 bars. Used for the "nav-toggle".
`=loader`	Creates a CSS-only loading spinner. Used for the ".loader" element, and for input and button spinners.
`=overflow-touch`	Sets the style of a container so that it keeps momentum when scrolling on iOS devices.
`=overlay($offset: 0)`	Makes the element overlay its parent container, like the transparent modal background.
`=placeholder`	Sets the styles of an input placeholder.
`=unselectable`	Turns the element unselectable. Used for buttons to prevent selection when clicking.