Get familiar with what is Sass and how you can customize your theme using Sass variables, maps, and functions defined by Propeller.


Sass stands for Syntactically Awesome Stylesheets Sass. It's a way to write the CSS using variables, nested rules, and functions which encourages reusability and makes development and maintenance task easier.

For instance, to change the color of an item in all the pages, you have to search it everywhere and make the necessary changes. But now, theming is accomplished by Sass variables and Sass maps. So, changing the value of one variable will apply changes wherever needed.


Use Propeller source Sass files to take advantage of variables, maps, mixins, and more.

File Structure

If you’ve downloaded our source files, you will have to manually setup a folder structure similar to this.



In your custom.scss, you’ll have to import Propeller’s source Sass files. You have two options available to include Propeller Sass Files: either import all or pick the standalone parts as per your requirement. For beginners, we suggest using the full import stack from our propeller.scss file.



With that setup in place, you can begin to modify any of the Sass variables and maps in your custom.scss.

Variable Defaults

A lot of customization in your theme can be done using the Propeller's pre-defined variables. You can find all the pre-defined variables in the _variables.scss file.

Every Propeller Sass variable includes a !default flag which depicts default values of the variables. Just copy and paste the variables to be modified in your file and modify their values.

While overriding the variables in same file, it doesn't matter whether they are overridden before or after the definition of default variables. However, if you are overriding the Sass variables in your files, override them before you import the Propeller's Sass files.

For example, to change background-color and color of the body tag, just call the variable above the import in your file as shown below:


You can modify all the variables including the global options by repeating the same process.

Maps and Loops

Propeller has defined a few Sass Maps, the key-value pairs to make it easier and faster to generate families of related CSS. We have used Sass Maps for our colors.

Just like Sass variables, Sass Maps also have default values which can be overridden by defining them in your custom.scss file.

Modify Map

To modify an existing color in our $theme-colors map, add the following to your custom Sass file:


Add Map

To add a new color to $theme-colors, add the new key and value:


Required Keys

Some of the keys are important to be present in the Sass Maps as we have used them in different places. So modifying their default values might not create any problem but removing them can lead to Sass compilation issues. In this case, you might need to modify the Sass code where these values are used.


Propeller uses the following function for getting values from the theme-colors map:


This function allows you to pick one color from a Sass map which is similar to defining a custom class for a particular color like .red.


Propeller also has a function to get a particular level of a color from the $theme-colors map same as in Bootstrap 4. Negative level values will lighten the color, while higher levels will darken it.


For example, to get a particular shade of your primary color, you just need to call the function in your file and pass the two parameters: primary and the numeric level of that shade.


Color Contrast

We have also included the color contrast function .color-yiq same as in Bootstrap 4. This function automatically returns a light (#fff) or dark (#111) contrast color based on the specified base color. This function is mainly useful for mixins or loops where you’re generating multiple classes.

For example, to generate color swatches from our $theme-colors map:


It can also be used for one-off contrast needs:


You can also specify a base color with our color map functions:


Box Shadow

As per the Google's Material Design standards, every component has a depth which determines how far or raised the element is from the page. So, We have included a new function box-shadow to set the z-depth of the components. This function automatically returns a box-shadow value of the component.

Following is the function defined for the same:


You can use the function in the following way:



Various Propeller components use a series of colors defined in the Sass map. This map can be looped over in Sass to quickly generate a series of rulesets.

Theme colors

The color scheme of Propeller is defined in the $theme-colors Sass map or by using Sass variables such as primary, success, etc in our scss/_variables.scss file. You can modify these variables to define the color pallette of your project.


Create or overwrite the variables within the Sass map to update the look and feel of your theme components.


Many Propeller components are built with @each loops that iterate over a Sass map which helps in generating the variants very easily. As you modify these Sass maps and recompile them, all the changes will be reflected in these loops.


Many of Propeller’s components are built with a base-modifier class approach which means most of the stying in contained in the main component class like .btn and the style variations are contained in their modifier classes like .btn-success. These modifier classes are built from the $theme-colors map to make customizing the number and name of our modifier classes.

Here is an example of how we loop over the $theme-colors map to generate modifiers to the .btn component.