## Skeleton SASS

For all the SASS lovers out there, we have converted a Dave Gamache's Skeleton CSS into SASS! The official repository can be found here: https://github.com/atomicpages/skeleton-sass.

## Features

• SASS + Compass translation
• SASS translation
• .scss and .sass files
• A demo file showcasing the features of Skeleton SASS
• A testing file that displays the default styling for the framework

Use Skeleton SASS on your next project!

Note: any corrections on this project please see start a pull request or create an issue.

## Intro to SASS - Nesting and Selector Inheritance

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SASS is a way to create dynamic styles that render into CSS. SASS is a better way to write and manage styles because of nesting and selector inheritance. Without further ado, let's learn more about SASS!

### Nesting in SASS

Nesting selectors in SASS provides a more organized approach to writing styles. In SASS, nesting selectors allows for a style sheet that resembles your DOM structure instead of normal CSS. The best way to learn about nesting is by example:

&lt;div class=&quot;foo&quot;&gt;
&lt;div class=&quot;bar&quot;&gt;&amp;nbsp&lt;/div&gt;
&lt;/div&gt;

.foo {
background: white;
.bar {
background: black;
}
}

/* CSS OUTPUT */
/* .foo { background: white; } */
/* .foo .bar { background: black; } */


If we place our source code and SASS script back-to-back we will see:

 

 .foo { background: white; .bar { // .bar is a child of .foo background: black; } } 

We can easily see how SASS strives to duplicate the DOM structure and give people an idea of how the elements are nested within the DOM.

The only magic to utilizing this method is to simply change how your code is written. Instead of indicating a parent-child relationship via .foo .bar (as we might do in conventional CSS) we can physically write .bar inside of .foo as the example above suggests.

Here are more complex examples:

&lt;div class=&quot;block&quot;&gt;
&lt;p&gt;Foo bar&lt;/p&gt;
&lt;div class=&quot;inner&quot;&gt;
&lt;img src=&quot;foo.jpg&quot; alt=&quot;Foo Bar&quot;&gt;
&lt;p&gt;Foo Bar Image&lt;/p&gt;
&lt;/div&gt;
&lt;/div&gt;

div.block {
width: 150px;
height: 150px;
background: rgba(0,0,0,0.25);
p {
font-size: 10px;
color: white;
}
.inner {
margin: 0 auto;
text-align: center;
background: rgba(255,255,255,0.1);
border: 1px solid rgba(0,0,0,0.25);
p {
background: rgba(0,0,0,0.5);
color: #ff9300; /* overrides div.block p */
text-shadow: 0 0 1px 2px black;
}
}
}


Dissecting the code, we have an idea of our DOM structure:

We could explain the relationship in English as well:

• div.block has a child called p
• div.block has a child called .inner
• .inner has a child called p

Stressing a parental relationship:

• p has a parent called div.block
• .inner has a parent called div.block
• p has a parent called .inner
• p has a grandparent called div.block

Given the relationship above, we can predict the CSS output and where our defined styles will be applied to. For instance, p will have the styles we defined if p is a child of div.block.

Here is our CSS result:

div.block {
width: 150px;
height: 150px;
background: rgba(0, 0, 0, 0.25);
}

div.block p {
font-size: 10px;
color: white;
}

div.block .inner {
margin: 0 auto;
text-align: center;
background: rgba(255, 255, 255, 0.1);
border: 1px solid rgba(0, 0, 0, 0.25);
}
div.block .inner p {
background: rgba(0, 0, 0, 0.5);
color: #ff9300; /* overrides div.block p */
text-shadow: 0 0 1px 2px black;
}


#### Referencing Parent Selectors

SASS offers the ability to reference parent selectors which enables us quickly add styles without unnecessary repetition.

When referencing parent selectors we must use nested syntax and the & (ampersand).

Note: the ampersand & is a reserved character in SASS, if you need a literal & then use \0026

.foo {
color: white;
&amp;:hover {
color: black;
}
}


This is a very simple example of referencing a parent selector and using the pseudo-class :hover. Our output is:

.foo { color: white; }
.foo:hover { color: black; }


Initially, it might be difficult to grasp how convenient this can be. Let's see a better example!
Below is a snippet from Dave Gamache's Skeleton CSS Framework

.button,
button,
input[type=&quot;submit&quot;],
input[type=&quot;reset&quot;],
input[type=&quot;button&quot;] {
background: #eeeeee linear-gradient(top, rgba(255, 255, 255, 0.2) 0%, rgba(0, 0, 0, 0.2) 100%);
background: #eeeeee -moz-linear-gradient(top, rgba(255, 255, 255, 0.2) 0%, rgba(0, 0, 0, 0.2) 100%);
background: #eeeeee -ms-linear-gradient(top, rgba(255, 255, 255, 0.2) 0%, rgba(0, 0, 0, 0.2) 100%);
background: #eeeeee -o-linear-gradient(top, rgba(255, 255, 255, 0.2) 0%, rgba(0, 0, 0, 0.2) 100%);
background: #eeeeee -webkit-gradient(linear, left top, left bottom, color-stop(0%, rgba(255, 255, 255, 0.2)), color-stop(100%, rgba(0, 0, 0, 0.2)));
background: #eeeeee -webkit-linear-gradient(top, rgba(255, 255, 255, 0.2) 0%, rgba(0, 0, 0, 0.2) 100%);
background: #eeeeee;
border: 1px solid #aaaaaa;
border-left: 1px solid #cccccc;
border-top: 1px solid #cccccc;
color: #444444;
cursor: pointer;
display: inline-block;
font-family: &quot;HelveticaNeue&quot;, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif;
font-size: 11px;
font-weight: bold;
line-height: normal;
margin-bottom: 20px;
text-decoration: none;
text-shadow: 0 1px rgba(255, 255, 255, 0.75);
}
.button:hover,
button:hover,
input[type=&quot;submit&quot;]:hover,
input[type=&quot;reset&quot;]:hover,
input[type=&quot;button&quot;]:hover {
background: #dddddd linear-gradient(top, rgba(255, 255, 255, 0.3) 0%, rgba(0, 0, 0, 0.3) 100%);
background: #dddddd -moz-linear-gradient(top, rgba(255, 255, 255, 0.3) 0%, rgba(0, 0, 0, 0.3) 100%);
background: #dddddd -ms-linear-gradient(top, rgba(255, 255, 255, 0.3) 0%, rgba(0, 0, 0, 0.3) 100%);
background: #dddddd -o-linear-gradient(top, rgba(255, 255, 255, 0.3) 0%, rgba(0, 0, 0, 0.3) 100%);
background: #dddddd -webkit-gradient(linear, left top, left bottom, color-stop(0%, rgba(255, 255, 255, 0.3)), color-stop(100%, rgba(0, 0, 0, 0.3)));
background: #dddddd -webkit-linear-gradient(top, rgba(255, 255, 255, 0.3) 0%, rgba(0, 0, 0, 0.3) 100%);
background: #dddddd;
border: 1px solid #888888;
border-left: 1px solid #aaaaaa;
border-top: 1px solid #aaaaaa;
color: #222222;
}
.button:active,
button:active,
input[type=&quot;submit&quot;]:active,
input[type=&quot;reset&quot;]:active,
input[type=&quot;button&quot;]:active {
background: #cccccc linear-gradient(top, rgba(255, 255, 255, 0.35) 0%, rgba(10, 10, 10, 0.4) 100%);
background: #cccccc -moz-linear-gradient(top, rgba(255, 255, 255, 0.35) 0%, rgba(10, 10, 10, 0.4) 100%);
background: #cccccc -ms-linear-gradient(top, rgba(255, 255, 255, 0.35) 0%, rgba(10, 10, 10, 0.4) 100%);
background: #cccccc -o-linear-gradient(top, rgba(255, 255, 255, 0.35) 0%, rgba(10, 10, 10, 0.4) 100%);
background: #cccccc -webkit-gradient(linear, left top, left bottom, color-stop(0%, rgba(255, 255, 255, 0.35)), color-stop(100%, rgba(10, 10, 10, 0.4)));
background: #cccccc -webkit-linear-gradient(top, rgba(255, 255, 255, 0.35) 0%, rgba(10, 10, 10, 0.4) 100%);
background: #cccccc;
border: 1px solid #666666;
}
.button.full-width,
button.full-width,
input[type=&quot;submit&quot;].full-width,
input[type=&quot;reset&quot;].full-width,
input[type=&quot;button&quot;].full-width {
text-align: center;
width: 100%;
}


As wonderful of a framework as this is, we can translate this into a SASS script and see the power of referencing parent selectors:

.button,
button,
input[type=&quot;submit&quot;],
input[type=&quot;reset&quot;],
input[type=&quot;button&quot;] {
background: #eeeeee linear-gradient(top, rgba(255, 255, 255, 0.2) 0%, rgba(0, 0, 0, 0.2) 100%);
background: #eeeeee -moz-linear-gradient(top, rgba(255, 255, 255, 0.2) 0%, rgba(0, 0, 0, 0.2) 100%);
background: #eeeeee -ms-linear-gradient(top, rgba(255, 255, 255, 0.2) 0%, rgba(0, 0, 0, 0.2) 100%);
background: #eeeeee -o-linear-gradient(top, rgba(255, 255, 255, 0.2) 0%, rgba(0, 0, 0, 0.2) 100%);
background: #eeeeee -webkit-gradient(linear, left top, left bottom, color-stop(0%, rgba(255, 255, 255, 0.2)), color-stop(100%, rgba(0, 0, 0, 0.2)));
background: #eeeeee -webkit-linear-gradient(top, rgba(255, 255, 255, 0.2) 0%, rgba(0, 0, 0, 0.2) 100%);
background: #eeeeee;
border: 1px solid #aaaaaa;
border-left: 1px solid #cccccc;
border-top: 1px solid #cccccc;
color: #444444;
cursor: pointer;
display: inline-block;
font-family: &quot;HelveticaNeue&quot;, &quot;Helvetica Neue&quot;, Helvetica, Arial, sans-serif;
font-size: 11px;
font-weight: bold;
line-height: normal;
margin-bottom: 20px;
text-decoration: none;
text-shadow: 0 1px rgba(255, 255, 255, 0.75);
&amp;:hover {
background: #dddddd linear-gradient(top, rgba(255, 255, 255, 0.3) 0%, rgba(0, 0, 0, 0.3) 100%);
background: #dddddd -moz-linear-gradient(top, rgba(255, 255, 255, 0.3) 0%, rgba(0, 0, 0, 0.3) 100%);
background: #dddddd -ms-linear-gradient(top, rgba(255, 255, 255, 0.3) 0%, rgba(0, 0, 0, 0.3) 100%);
background: #dddddd -o-linear-gradient(top, rgba(255, 255, 255, 0.3) 0%, rgba(0, 0, 0, 0.3) 100%);
background: #dddddd -webkit-gradient(linear, left top, left bottom, color-stop(0%, rgba(255, 255, 255, 0.3)), color-stop(100%, rgba(0, 0, 0, 0.3)));
background: #dddddd -webkit-linear-gradient(top, rgba(255, 255, 255, 0.3) 0%, rgba(0, 0, 0, 0.3) 100%);
background: #dddddd;
border: 1px solid #888888;
border-left: 1px solid #aaaaaa;
border-top: 1px solid #aaaaaa;
color: #222222;
}
&amp;:active {
background: #cccccc linear-gradient(top, rgba(255, 255, 255, 0.35) 0%, rgba(10, 10, 10, 0.4) 100%);
background: #cccccc -moz-linear-gradient(top, rgba(255, 255, 255, 0.35) 0%, rgba(10, 10, 10, 0.4) 100%);
background: #cccccc -ms-linear-gradient(top, rgba(255, 255, 255, 0.35) 0%, rgba(10, 10, 10, 0.4) 100%);
background: #cccccc -o-linear-gradient(top, rgba(255, 255, 255, 0.35) 0%, rgba(10, 10, 10, 0.4) 100%);
background: #cccccc -webkit-gradient(linear, left top, left bottom, color-stop(0%, rgba(255, 255, 255, 0.35)), color-stop(100%, rgba(10, 10, 10, 0.4)));
background: #cccccc -webkit-linear-gradient(top, rgba(255, 255, 255, 0.35) 0%, rgba(10, 10, 10, 0.4) 100%);
background: #cccccc;
border: 1px solid #666666;
}
&amp;.full-width {
text-align: center;
width: 100%;
}
}


Our end result will be identical so why is this so awesome anyway? Consider we needed to add an element to this list. Using pure CSS we will need to add the extra element three or four times before it is applied. Using SASS, however, we can add it once and with referencing parent selectors we can let the compiler figure the everything out.

Another feature of SASS, similar to vanilla CSS, is we have the ability to group selectors, even when referencing a parent or utilizing the alternative syntax.

nav {
ul {
margin: 0;
li {
list-style: none;
float: left;
margin-right: 10px;
&amp;:hover, // grouping for li:hover and li.active
&amp;.active { background: rgba(255,255,255,0.4); }
a {
color: #ff9300;
text-decoration: underline;
&amp;:hover, // a:hover
&amp;:active, // a:active
&amp;.active { // a.active
color: #804a00;
text-decoration: none;
}
}
}
}
}


And our CSS rendering:

nav ul {
margin: 0;
}
nav ul li {
list-style: none;
float: left;
margin-right: 10px;
}
nav ul li:hover,
nav ul li.active { background: rgba(255, 255, 255, 0.4); }
nav ul li a {
color: #ff9300;
text-decoration: underline;
}
nav ul li a:hover,
nav ul li a:active,
nav ul li a.active {
color: #804a00;
text-decoration: none;
}


#### Nested Properties

Nested properties is an interesting feature of SASS. This enables us to use a single basic property and literally split it up into its individual properties. Let's say, for instance, we look at the margin property. We can define this particular property several different ways:

html {
/* Condensed form */
margin: [top] [right] [bottom] [left];
margin: [top] [right/left] [bottom];
margin: [top/bottom] [right/left];
margin: [top/right/bottom/left];

/* Individual */
margin-top: [top];
margin-right: [right];
margin-bottom: [bottom];
margin-left: [left];
}


Looking at the margin we clearly see many different ways to get the same result. The condensed form is a single property while the individual forms are four separate properties. In SASS, we can isolate these four properties by identifying the margin parent property and then defining each child property separately. Here is what we mean:

body {
margin: {
top: 4px;
right: 5px;
bottom: 6px;
left: 7px;
};
}


Bizarre—no?
Nested properties is yet another way to define properties with multiple sub-properties in that nested-style syntax that keeps coming back. Not surprisingly, our result will be:

body {
margin-top: 4px;
margin-right: 5px;
margin-bottom: 6px;
margin-left: 7px;
}


Here are more examples:

body {
font: {
family: &quot;Trebuchet MS&quot;, Tahoma, Arial, sans-serif;
size: 2em;
weight: bold;
style: italic;
}
}


Will render to:

body {
font-family: &quot;Trebuchet MS&quot;, Tahoma, Arial, sans-serif;
font-size: 2em;
font-weight: bold;
font-style: italic;
}


## Bitwise Algorithm 4: Find Odd Singleton

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### Problem

Given an array of integers, in which all values occur an even number of times except for one which occurs an odd number of times. Find the integer that occurs an odd number of times.

For example, given this array: $4, 5, 7, 3, 4, 4, 4, 7, 3, 5, 7$. The number 7 occurs an odd number of times while every other number occurs an even number of times, so the solution is 7.

### Algorithm

My first thought when hearing this problem was to create an dictionary/hashmap to keep track of the count of each number and then just find the one with an odd count and return the corresponding number. This is a perfectly good solution that runs in $O(n)$ time and also requires $O(n)$ space (where $n$ is the size of the array). $O(n)$ is definitely the best we can do with time, because it would be impossible to solve the problem without looking at every number in the array, but we can do better with space using some bitwise operations!

Recall the bitwise XOR operator from boolean algebra. If you bitwise XOR a number with itself, you get 0. If you bitwise XOR a number with 0, you get the original number. If we XOR all the numbers in the array together, we are left with just the bits from the value that appears an odd number of times (since it didn't have a pair to cancel out with).

In our example:
4 XOR 5 = 1
1 XOR 7 = 6
6 XOR 3 = 5
5 XOR 4 = 1
1 XOR 4 = 5
5 XOR 4 = 1
1 XOR 7 = 6
6 XOR 3 = 5
5 XOR 5 = 0
0 XOR 7 = 7

As expected, the number we are left with is 7.

Here is the code in java:

public static int findOddSingleton(int[] nums) {
int n = nums[0];
for (int i = 1; i < nums.length; i++)
n = n ^ nums[i];
}
return n;
}


## Bitwise Algorithm 3: Count Bits

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### Problem

Count the number of 1s in the bit representation of the given integer.

For example, given the number $6$, the bit representation is $0110$, which contains two 1s, so the answer is $2$.

### Algorithm

In the previous tutorial we learned how to clear the lowest bit of a number. We can use that algorithm to solve this problem. All we need to do is count how many times we need to clear the lowest bit of a number, until we are left with the number 0.

Here is the code in java:

public static int countBits(int n, int k) {
int count = 0;
while(0 != n) {
n = clearLowestBit(n);
count++;
}
return count;
}


## Bitwise Algorithm 2: Clear Lowest Bit

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### Problem

Clear the rightmost set bit in the given integer.

For example, given the number $5$, the bit pattern is $0101$. Clearing the right most set bit we get $0100$, which is $4$. Given the number $8$, the bit pattern is $1000$, clearing the right most set bit we get $0$.

### Algorithm

The algorithm is simple. The difference in bit pattern between two consecutive binary numbers ($n$ and $n-1$) is such that the rightmost set bit in the greater number is not set in the lesser number. However, all bits to the left of the rightmost set bit in the greater number are the same in both numbers. Therefore, if we bitwise AND the two consequence numbers together, we get the number in which the rightmost set bit from the greater number is unset, but all the other bits are kept the same.

Here is the code in java:

public static int clearLowestBit(int x) {
return x &amp; (x-1);
}

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