It's `rem` all the way. The base font size is defined as `px`-based variable and set once the `html` root element. All other font sizes and spacing values are set as `rem` units, being nicely relative to the root font size.
Just write the official, unprefixed syntax for all CSS 3 features, no need to write the vendor prefixed versions.
[Autoprefixer](https://github.com/postcss/autoprefixer) handles that for you automatically based on the browser versions defined in the task and data from [Can I Use](http://caniuse.com/).
SVG sprite
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All icons and most assets are SVGs. A gulp task grabs all svg files from the `img/` folder and puts them as `<symbol>` into one SVG sprite file. Reference those icons with the SVG `<use>` element and their ID in the HTML where you want them to be:
