Using default bootstrap variables.

How can I use default Boostrap variables for styling?

For example (from bootstrap/scss/_variables.scss):

$font-size-base:              1rem !default; // Assumes the browser default, typically `16px`
$font-size-lg:                $font-size-base * 1.25 !default;
$font-size-sm:                $font-size-base * .875 !default;

$font-weight-lighter:         lighter !default;
$font-weight-light:           300 !default;
$font-weight-normal:          400 !default;
$font-weight-bold:            700 !default;
$font-weight-bolder:          bolder !default;

Start there and if that doesn't have your answers, reply again. I don't do SASS yet, but others do so someone should be able to help more if that tutorial doesn't cover it.