How do I create dynamic CSS in Rails?
In Rails 3.1, you can have your stylesheets pre-processed by erb.
Now let's say you have some dynamic styling called dynamic.css.scss.erb (the .erb at the end is important!) in app/assets/stylesheets. It will be processed by erb (and then by Sass), and as such can contain stuff like
.some_container {
<% favorite_tags do |tag, color| %>
.tag.<%= tag %=> {
background-color: #<%= color %>;
}
<% end %>
}
You can include it like any stylesheet.
How dynamic should it be?
Note that it will be only processed once, though, so if the values changes, the stylesheet won't.
I don't think there is a super efficient way to do have it completely dynamic yet, but it is still possible to generate the CSS for all requests. With this caveat in mind, here's a helper for that in Rails 3.1:
def style_tag(stylesheet)
asset = YourApplication::Application.assets[stylesheet]
clone = asset.class.new(asset.environment, asset.logical_path, asset.pathname, {})
content_tag("STYLE", clone.body.html_safe, type:"text/css")
end
Here's how to use it:
First, copy the above helper in app/helpers/application_helper.rb.
You can then include it in your page as follows:
<% content_for :head do %>
<%= style_tag "dynamic.css" %>
<% end %>
The rest of your page.
Make sure that your layout uses the content :head. For example, your layout/application.html.erb could look like:
...
<HEAD>
....
<%= yield :head %>
</HEAD>
...
I found this out thanks to this post.
There has been a lot of development over the years, and I recently figured out how to do what this question is asking. And since it has been about 9-10 years since someone has answered this, I thought that I would put in my 2 cents.
As others have said, it is not good practice, and thus can not be done, to put ruby code directly into the CSS file as the CSS is precompiled and is not able to be dynamically changed within the file.... BUT, it can be dynamically changed outside the file!
I will need to give a quick synopsis of CSS variables in case future readers do not know how to use them.
CSS has the use of variables within its coding language to make it easier to change a lot of elements at one time. You put these variables at the top of the CSS file in a root section. Like this:
:root {
--primary: #0061f2;
--secondary: #6900c7;
}
Now, anytime you want to style an element one of those colors, you can simply put var(--variableName) like this:
.btn{
color: var(--secondary);
background-color: var(--primary);
}
.h1 {
color: var(--primary);
}
You can see how it would then be much easier to change the variable in the root section and thus change all other instances within the CSS.
Now for the dynamic Ruby part.
In the <head> section of your application file (or in the case of this question the file that holds the template for the admin's dashboard), you will need to redeclare the CSS variables with your dynamic variables and mark them as important. For example, let's say that you allow your user to choose primary and secondary colors for their dashboard and they are stored in the user's profile called like: user.primary_color and user.secondary_color. You will need to add this to your <head> section:
<style>
:root{
--primary: <%= user.primary_color %> !important;
--secondary: <%= user.secondary_color %> !important;
}
</style>
This !important tag will override the variables found in the CSS file thus dynamically allowing the user to change the CSS and view of their dashboard and have it remain persistent (as the values are saved in their profile).
I hope that this helps future developers.
Happy Coding!
You can use ERB with CSS, you just need to render css in the controller. However, for such a heavily requested resource, I do not recommend generating this every time. I would store the users stylesheet in memcached or redis, and recall from it when the page loads, rather than rerendering the file each time. When they update their style, you can expire the cache, just make sure it gets rebuilt when the page renders.