Not able to find pre-defined sass variables in Jekyll project - ruby

Question

I'm new the Jeykll and Sass and have a quick question. Within the pre-built theme when starting a new project, where are these variables defined?
I can't seem to find them aware through out the build.
This is in the _sass/layout.scss directory.
*/
.site-header {
border-top: 5px solid $grey-color-dark;
border-bottom: 1px solid $grey-color-light;
min-height: 56px;
// Positioning context for the mobile navigation icon
position: relative;
}
.site-title {
font-size: 26px;
line-height: 56px;
letter-spacing: -1px;
margin-bottom: 0;
float: left;
&,
&:visited {
color: $grey-color-dark;
}
}
.site-nav {
float: right;
line-height: 56px;
.menu-icon {
display: none;
}
.page-link {
color: $text-color;
line-height: $base-line-height;
// Gaps between nav items, but not on the first one
&:not(:first-child) {
margin-left: 20px;
}
}
#include media-query($on-palm) {
position: absolute;
top: 9px;
right: 30px;
background-color: $background-color;
border: 1px solid $grey-color-light;
border-radius: 5px;
text-align: right;
.menu-icon {
display: block;
float: right;
width: 36px;
height: 26px;
line-height: 0;
padding-top: 10px;
text-align: center;
> svg {
width: 18px;
height: 15px;
path {
fill: $grey-color-dark;
}
}
}
.trigger {
clear: both;
display: none;
}
&:hover .trigger {
display: block;
padding-bottom: 5px;
}
.page-link {
display: block;
padding: 5px 10px;
}
}
}
/**
* Site footer
*/
.site-footer {
border-top: 1px solid $grey-color-light;
padding: $spacing-unit 0;
}
.footer-heading {
font-size: 18px;
margin-bottom: $spacing-unit / 2;
}
.contact-list,
.social-media-list {
list-style: none;
margin-left: 0;
}
.footer-col-wrapper {
font-size: 15px;
color: $grey-color;
margin-left: -$spacing-unit / 2;
#extend %clearfix;
}
.footer-col {
float: left;
margin-bottom: $spacing-unit / 2;
padding-left: $spacing-unit / 2;
}
.footer-col-1 {
width: -webkit-calc(35% - (#{$spacing-unit} / 2));
width: calc(35% - (#{$spacing-unit} / 2));
}
.footer-col-2 {
width: -webkit-calc(20% - (#{$spacing-unit} / 2));
width: calc(20% - (#{$spacing-unit} / 2));
}
.footer-col-3 {
width: -webkit-calc(45% - (#{$spacing-unit} / 2));
width: calc(45% - (#{$spacing-unit} / 2));
}
#include media-query($on-laptop) {
.footer-col-1,
.footer-col-2 {
width: -webkit-calc(50% - (#{$spacing-unit} / 2));
width: calc(50% - (#{$spacing-unit} / 2));
}
.footer-col-3 {
width: -webkit-calc(100% - (#{$spacing-unit} / 2));
width: calc(100% - (#{$spacing-unit} / 2));
}
}
#include media-query($on-palm) {
.footer-col {
float: none;
width: -webkit-calc(100% - (#{$spacing-unit} / 2));
width: calc(100% - (#{$spacing-unit} / 2));
}
}
/**
* Page content
*/
.page-content {
padding: $spacing-unit 0;
}
.page-heading {
font-size: 20px;
}
.post-list {
margin-left: 0;
list-style: none;
> li {
margin-bottom: $spacing-unit;
}
}
.post-meta {
font-size: $small-font-size;
color: $grey-color;
}
.post-link {
display: block;
font-size: 24px;
}
/**
* Posts
*/
.post-header {
margin-bottom: $spacing-unit;
}
.post-title {
font-size: 42px;
letter-spacing: -1px;
line-height: 1;
#include media-query($on-laptop) {
font-size: 36px;
}
}
.post-content {
margin-bottom: $spacing-unit;
h2 {
font-size: 32px;
#include media-query($on-laptop) {
font-size: 28px;
}
}
h3 {
font-size: 26px;
#include media-query($on-laptop) {
font-size: 22px;
}
}
h4 {
font-size: 20px;
#include media-query($on-laptop) {
font-size: 18px;
}
}
}

Answer 1

Notice: Jekyll has since been updated, its default theme, minima, is now in a separate gem, and the definitions are there, in _sass/minima.scss.
Look at this, with relative path to site root in default Jekyl site css/main.scss. There they are. After all the definitions, imports and processing, there will be css/main.css in the resulting site.
Everything in _sass is just for importing into real assets that will be converted to CSS. The difference between Sass/SCSS files in _sass and everywhere else is that files from _sass are not compiled directly, but rather just lay where they are and wait to be imported. Every possibly reusable piece of Sass should be in _sass, that's what Sass partials and this system overall is designed for. This is especially useful if you use a lot of Sass libraries (like I do, and it's still a mess) and don't want them to be modified in order to be put into your assets.
All the other files (not in _sass), however, will be processed into corresponding *.css files, and in order to distinguish files for processing, Jekyll requires such files to have a YAML front-matter, usually empty.
---
---
// Sass code here
(I used to utilize Liquid for embedding variables in Sass, but that feature vanished after some updates, so now non-empty YFM in assets is of no use now).