Theming Melvin
Customize Melvin 4 with our new built-in Sass variables for global style preferences for easy theming and component changes.
Introduction
In Melvin, theming is accomplished by Sass variables, Sass maps, and custom CSS. There’s no more dedicated theme stylesheet; instead, you can enable the built-in theme to add gradients, shadows, and more.
Sass
Utilize our source Sass files to take advantage of variables, maps, mixins, and more.
File structure
You’ll have a file structure that looks like this:
If you’ve downloaded our source files and aren’t using a package manager, you’ll want to manually setup something similar to this structure.
Variable defaults
Every Sass variable in Melvin 4 allow you to modify the variable’s value in your own Sass. If a variable has already been assigned, then it won’t be re-assigned by the default values in Melvin.
You will find the complete list of Melvin’s variables in style/_variables.scss
.
Here’s an example that changes the background-color
and color
for the <body>
when importing and compiling Melvin via gulp:
Repeat as necessary for any variable in Melvin, including the global options below.
Maps and loops
Melvin 4 includes a handful of Sass maps, key value pairs that make it easier to generate families of related CSS. We use Sass maps for our colors, grid breakpoints, and more. Just like Sass variables.
Some of our Sass maps are merged into empty ones by default. This is done to allow easy expansion of a given Sass map, but comes at the cost of making removing items from a map slightly more difficult.
Modify map
To modify an existing color in our $theme-colors
map, add the following to your custom Sass file:
Add to map
To add a new color to $theme-colors
, add the new key and value:
Remove from map
To remove colors from $theme-colors
, or any other map, use map-remove
.
Required keys
Melvin assumes the presence of some specific keys within Sass maps as we used and extend these ourselves. As you customize the included maps, you may encounter errors where a specific Sass map’s key is being used.
For example, we use the primary
, success
, and danger
keys from $theme-colors
for links, buttons, and form states. Replacing the values of these keys should present no issues, but removing them may cause Sass compilation issues. In these instances, you’ll need to modify the Sass code that makes use of those values.
Functions
Melvin utilizes several Sass functions, but only a subset are applicable to general theming. We’ve included three functions for getting values from the color maps:
These allow you to pick one color from a Sass map much like how you’d use a color variable from v3.
We also have another function for getting a particular level of color from the $theme-colors
map. Negative level values will lighten the color, while higher levels will darken.
In practice, you’d call the function and pass in two parameters: the name of the color from $theme-colors
(e.g., primary or danger) and a numeric level.
Additional functions could be added in the future or your own custom Sass to create level functions for additional Sass maps, or even a generic one if you wanted to be more verbose.
Color contrast
One additional function we include in Melvin is the color contrast function, color-yiq
. It utilizes the YIQ color space to automatically return a light (#fff
) or dark (#111
) contrast color based on the specified base color. This function is especially 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:
Sass options
Customize Melvin 4 with our built-in custom variables file and easily toggle global CSS preferences with new $enable-*
Sass variables. Override a variable’s value and recompile with npm run test
as needed.
You can find and customize these variables for key global options in Melvin’s scss/_variables.scss
file.
Variable | Values | Description |
---|---|---|
$spacer |
1rem (default), or any value > 0 |
Specifies the default spacer value to programmatically generate our spacer utilities. |
$enable-rounded |
true (default) or false |
Enables predefined border-radius styles on various components. |
$enable-shadows |
true or false (default) |
Enables predefined box-shadow styles on various components. |
$enable-gradients |
true or false (default) |
Enables predefined gradients via background-image styles on various components. |
$enable-transitions |
true (default) or false |
Enables predefined transition s on various components. |
$enable-hover-media-query |
true or false (default) |
Deprecated |
$enable-grid-classes |
true (default) or false |
Enables the generation of CSS classes for the grid system (e.g., .container , .row , .col-md-1 , etc.). |
$enable-caret |
true (default) or false |
Enables pseudo element caret on .dropdown-toggle . |
$enable-print-styles |
true (default) or false |
Enables styles for optimizing printing. |
Color
Many of Melvin’s various components and utilities are built through a series of colors defined in a Sass map. This map can be looped over in Sass to quickly generate a series of rulesets.
All colors
All colors available in Melvin 4, are available as Sass variables and a Sass map in scss/_variables.scss
file. This will be expanded upon in subsequent minor releases to add additional shades, much like the grayscale palette we already include.
Here’s how you can use these in your Sass:
Color utility classes are also available for setting color
and background-color
.
In the future, we’ll aim to provide Sass maps and variables for shades of each color as we’ve done with the grayscale colors below.
Theme colors
We use a subset of all colors to create a smaller color palette for generating color schemes, also available as Sass variables and a Sass map in Melvins’s scss/_variables.scss
file.
Grays
An expansive set of gray variables and a Sass map in scss/_variables.scss
for consistent shades of gray across your project.
Within scss/_variables.scss
, you’ll find Melvin’s color variables and Sass map. Here’s an example of the $colors
Sass map:
Add, remove, or modify values within the map to update how they’re used in many other components. Unfortunately at this time, not every component utilizes this Sass map. Future updates will strive to improve upon this. Until then, plan on making use of the ${color}
variables and this Sass map.
Components
Many of Melvin’s components and utilities are built with @each
loops that iterate over a Sass map. This is especially helpful for generating variants of a component by our $theme-colors
and creating responsive variants for each breakpoint. As you customize these Sass maps and recompile, you’ll automatically see your changes reflected in these loops.
Modifiers
Many of Melvin’s components are built with a base-modifier class approach. This means the bulk of the styling is contained to a base class (e.g., .btn
) while style variations are confined to modifier classes (e.g., .btn-danger
). These modifier classes are built from the $theme-colors
map to make customizing the number and name of our modifier classes.
Here are two examples of how we loop over the $theme-colors
map to generate modifiers to the .alert
component and all our .bg-*
background utilities.
Responsive
These Sass loops aren’t limited to color maps, either. You can also generate responsive variations of your components or utilities. Take for example our responsive text alignment utilities where we mix an @each
loop for the $grid-breakpoints
Sass map with a media query include.
Should you need to modify your $grid-breakpoints
, your changes will apply to all the loops iterating over that map.
CSS variables
Melvin 4 includes around two dozen CSS custom properties (variables) in its compiled CSS. These provide easy access to commonly used values like our theme colors, breakpoints, and primary font stacks when working in your browser’s Inspector, a code sandbox, or general prototyping.
Available variables
Here are the variables we include (note that the :root
is required). They’re located in our _root.scss
file.
Examples
CSS variables offer similar flexibility to Sass’s variables, but without the need for compilation before being served to the browser. For example, here we’re resetting our page’s font and link styles with CSS variables.
Breakpoint variables
While we originally included breakpoints in our CSS variables (e.g., --breakpoint-md
), these are not supported in media queries, but they can still be used within rulesets in media queries. These breakpoint variables remain in the compiled CSS for backward compatibility given they can be utilized by JavaScript. Learn more in the spec.
Here’s an example of what’s not supported:
And here’s an example of what is supported: