[css] Customizing Bootstrap CSS template

I am just getting started with Bootstrap from Twitter and am wondering what the ‘best practices’ is for customization. I want to develop a system that will take advantage of all the power of a css template (Bootstrap or other), be completely (and easily) modifiable, be sustainable (ie – when the next version of Bootstrap is released from Twitter I don’t have to start over.

For example, I want to add background images to the top navigation. It looks like there are 3 ways to go about this:

1. Modify the .topbar classes in bootstrap.css . I don’t particularly like this because I will have lots of .topbar items and I don’t necessarily want to modify them all the same way.
2. Create new classes with my background images and apply both styles (the new and the bootstrap to my element). This may create style conflicts, which could be avoided by stripping the .topbar class into separate classes and then only using the pieces that are not stepped on by my custom class. Again this requires more work than I think should be necessary and while it is flexible, it won’t allow me to easily update bootstrap.css when Twitter releases the next installment.
3. Use variables in .LESS to achieve the customization. Offhand this seems like a good approach but having not used .LESS I have concerns about compiling css on the client and about code sustainability.

Though I am using Bootstrap, this question can be generalized to any css template.

Thanks in advance for input.

you can start with this tool, https://themestr.app/theme , seeing how it overwrites the scss variables, you would get an idea what variable impacts what. its the simplest way I think.

example scss genearation:

@import url(https://fonts.googleapis.com/css?family=Montserrat:200,300,400,700);
$font-family-base:Montserrat;
@import url(https://fonts.googleapis.com/css?family=Open+Sans:200,300,400,700);
$headings-font-family:Open Sans;

$enable-grid-classes:false;
$primary:#222222;
$secondary:#666666;
$success:#333333;
$danger:#434343;
$info:#515151;
$warning:#5f5f5f;
$light:#eceeec;
$dark:#111111;
@import "bootstrap";

Since Pabluez's answer back in December, there is now a better way to customize Bootstrap.

Use: Bootswatch to generate your bootstrap.css

Bootswatch builds the normal Twitter Bootstrap from the latest version (whatever you install in the bootstrap directory), but also imports your customizations. This makes it easy to use the the latest version of Bootstrap, while maintaining custom CSS, without having to change anything about your HTML. You can simply sway boostrap.css files.

The best option in my opinion is to compile a custom LESS file including bootstrap.less, a custom variables.less file and your own rules :

1. Clone bootstrap in your root folder : git clone https://github.com/twbs/bootstrap.git
2. Rename it "bootstrap"
3. Create a package.json file : https://gist.github.com/jide/8440609
4. Create a Gruntfile.js : https://gist.github.com/jide/8440502
5. Create a "less" folder
6. Copy bootstrap/less/variables.less into the "less" folder
7. Change the font path : @icon-font-path: "../bootstrap/fonts/";
8. Create a custom style.less file in the "less" folder which imports bootstrap.less and your custom variables.less file : https://gist.github.com/jide/8440619
9. Run npm install
10. Run grunt watch

Now you can modify the variables any way you want, override bootstrap rules in your custom style.less file, and if some day you want to update bootstrap, you can replace the whole bootstrap folder !

EDIT: I created a Bootstrap boilerplate using this technique : https://github.com/jide/bootstrap-boilerplate

You can use the bootstrap template from

http://www.initializr.com/

which includes all the bootstrap .less files. You can then change variables / update the less files as you want and it will automatically compile the css. When deploying compile the less file to css.

Update 2019 - Bootstrap 4

I'm revisiting this Bootstrap customization question for 4.x, which now utilizes SASS instead of LESS. In general, there are 2 ways to customize Bootstrap...

1. Simple CSS Overrides

One way to customize is simply using CSS to override Bootstrap CSS. For maintainability, CSS customizations are put in a separate custom.css file, so that the bootstrap.css remains unmodified. The reference to the custom.css follows after the bootstrap.css for the overrides to work...

<link rel="stylesheet" type="text/css" href="css/bootstrap.min.css">
<link rel="stylesheet" type="text/css" href="css/custom.css">

Just add whatever changes are needed in the custom CSS. For example...

    /* remove rounding from cards, buttons and inputs */
    .card, .btn, .form-control {
        border-radius: 0;
    }

Before (bootstrap.css)

After (with custom.css)

When making customizations, you should understand CSS Specificity. Overrides in the custom.css need to use selectors that are the same specificity as (or more specific) the bootstrap.css.

Note there is no need to use !important in the custom CSS, unless you're overriding one of the Bootstrap Utility classes. CSS specificity always works for one CSS class to override another.

2. Customize using SASS

If you're familiar with SASS (and you should be to use this method), you can customize Bootstrap with your own custom.scss. There is a section in the Bootstrap docs that explains this, however the docs don't explain how to utilize existing variables in your custom.scss. For example, let's change the body background-color to #eeeeee, and change/override the blue primary contextual color to Bootstrap's $purple variable...

/* custom.scss */    

/* import the necessary Bootstrap files */
@import "bootstrap/functions";
@import "bootstrap/variables";

/* -------begin customization-------- */   

/* simply assign the value */ 
$body-bg: #eeeeee;

/* use a variable to override primary */
$theme-colors: (
  primary: $purple
);
/* -------end customization-------- */  

/* finally, import Bootstrap to set the changes! */
@import "bootstrap";

This also works to create new custom classes. For example, here I add purple to the theme colors which creates all the CSS for btn-purple, text-purple, bg-purple, alert-purple, etc...

/* add a new purple custom color */
$theme-colors: (
  purple: $purple
);

https://www.codeply.com/go/7XonykXFvP

With SASS you must @import bootstrap after the customizations to make them work! Once the SASS is compiled to CSS (this must be done using a SASS compiler node-sass, gulp-sass, npm webpack, etc..), the resulting CSS is the customized Bootstrap. If you're not familiar with SASS, you can customize Bootstrap using a tool like this theme builder I created.

Custom Bootstrap Demo (SASS)

Note: Unlike 3.x, Bootstrap 4.x doesn't offer an official customizer tool. You can however, download the grid only CSS or use another 4.x custom build tool to re-build the Bootstrap 4 CSS as desired.

Related:
How to extend/modify (customize) Bootstrap 4 with SASS
How to change the bootstrap primary color?
How to create new set of color styles in Bootstrap 4 with sass
How to Customize Bootstrap

I recently wrote a post about how I've been doing it at Udacity for the last couple years. This method has meant we've been able to update Bootstrap whenever we wanted to without having merge conflicts, thrown out work, etc. etc.

The post goes more in depth with examples, but the basic idea is:

• Keep a pristine copy of bootstrap and overwrite it externally.
• Modify one file (bootstrap's variables.less) to include your own variables.
• Make your site file @include bootstrap.less and then your overrides.

This does mean using LESS, and compiling it down to CSS before shipping it to the client (client-side LESS if finicky, and I generally avoid it) but it is EXTREMELY good for maintainability/upgradability, and getting LESS compilation is really really easy. The linked github code has an example using grunt, but there are many ways to achieve this -- even GUIs if that's your thing.

Using this solution, your example problem would look like:

• Change the nav bar color with @navbar-inverse-bg in your variables.less (not bootstrap's)
• Add your own nav bar styles to your bootstrap_overrides.less, overwriting anything you need to as you go.
• Happiness.

When it comes time to upgrade your bootstrap, you just swap out the pristine bootstrap copy and everything will still work (if bootstrap makes breaking changes, you'll need to update your overrides, but you'd have to do that anyway)

Blog post with walk-through is here.

Code example on github is here.

Use LESS with Bootstrap...

Here are the Bootstrap docs for how to use LESS

(they have moved since previous answers)

I think the officially preferred way is now to use Less, and either dynamically override the bootstrap.css (using less.js), or recompile bootstrap.css (using Node or the Less compiler).

From the Bootstrap docs, here's how to override bootstrap.css styles dynamically:

Download the latest Less.js and include the path to it (and Bootstrap) in the <head>.

 <link rel="stylesheet/less" href="/path/to/bootstrap.less">
    <script src="/path/to/less.js"></script>

To recompile the .less files, just save them and reload your page. Less.js compiles them and stores them in local storage.

Or if you prefer to statically compile a new bootstrap.css with your custom styles (for production environments):

Install the LESS command line tool via Node and run the following command:

$ lessc ./less/bootstrap.less > bootstrap.css