Apply a condition only on image which is nil Rails 4 - ruby-on-rails

Question

I'm new to Rails so my code is probably ugly..
I have a loop which give me the 3 latest articles on my index page.
I added a condition to say "if there is no image in my article, give me a image from unsplash".
The issue is : that's apply the condition on the 3 images even if 2 of 3 images exists. I want that only the image which is nil get the unsplash image.
How can I do that ?
<% #articles.last(3).in_groups_of(3, false).each do |group| %>
<div class="row">
<% group.each do |article| %>
<% if article.image.exists? %>
<div class="col-xs-12 col-sm-4">
<div class="card">
<style media>
.card { background: linear-gradient(-225deg, rgba(30,30,30,0.6) 30%, rgba(46,46,46,0.5) 80%), url("<%= article.image.url(:medium) %>"); }
</style>
<img src="<%= article.user.image.url(:thumb) %>" alt="" class="avatar-small card-user">
<div class="card-description">
<h3><%= article.title %></h3>
<p><%= truncate(article.subtitle, length: 45, escape: false) %></p>
</div>
</div>
</div>
<% else %>
<div class="col-xs-12 col-sm-4">
<div class="card">
<style media>
.card { background: linear-gradient(-225deg, rgba(30,30,30,0.6) 30%, rgba(46,46,46,0.5) 80%), url("http://unsplash.it/1280/500/?random"); }
</style>
<img src="<%= article.user.image.url(:thumb) %>" alt="" class="avatar-small card-user">
<div class="card-description">
<h3><%= article.title %></h3>
<p><%= truncate(article.subtitle, length: 45, escape: false) %></p>
</div>
</div>
</div>
<% end %>
<% end %>
</div>
<% end %>
my controller :
class PagesController < ApplicationController
def index
#articles = Article.last(3)
end
end
Thanks a lot for your help !

Answer 1

I finally find the error.
It was <style media> which was the issue.
I finally do this :
<% #articles.last(3).in_groups_of(3, false).each do |group| %>
<div class="row">
<% group.each do |article| %>
<div class="col-xs-12 col-sm-4">
<a href="<%= articles_path(article.slug) %>"><div style="background: linear-gradient(-225deg, rgba(30,30,30,0.6) 30%, rgba(46,46,46,0.5) 80%), url('<%= article.image.url(:thumb) %>');" class="card">
<img src="<%= article.user.image.url(:thumb) %>" alt="" class="avatar-small card-user">
<div class="card-description">
<h3><%= article.title %></h3>
<p><%= truncate(article.soustitre, length: 45, escape: false) %></p>
</div>
</div>
</div></a>
<% end %>
</div>
<% end %>
Now the 3 latest articles are displayed on my index page.
I add a default image with paperclip and withdrawed the condition if else.