Rails 開発環境で一部のCSSしか反映されない。Railsチュートリアル

前提・実現したいこと

Railsチュートリアル１３章をやっており、開発環境におけるCSSが一部しか読み込まれません。例えば.content（下記ソースコード参照）など一部は読み込まれますが、画像のように他のCSSは正常に読み込まれないです。原因は何が考えられるでしょうか？お力添えいただけると幸いです。

該当のソースコード

assets/stylesheets/custom.scss


/* microposts */

.microposts {
  list-style: none;
  padding: 0;
  li {
    padding: 10px 0;
    border-top: 1px solid #e8e8e8;
  }
  .user {
    margin-top: 5em;
    padding-top: 0;
  }
  .content {
    display: block;
    margin-left: 60px;
    img {
      display: block;
      padding: 5px 0;
    }
  }
  .timestamp {
    color: $gray-light;
    display: block;
    margin-left: 60px;
  }
  .gravatar {
    float: left;
    margin-right: 10px;
    margin-top: 5px;
  }
}

aside {
  textarea {
    height: 100px;
    margin-bottom: 5px;
  }
}

span.picture {
  margin-top: 10px;
  input {
    border: 0;
  }
}

config/environments/development.rb

Rails.application.configure do
  config.web_console.whitelisted_ips = '*********'
  config.cache_classes = false
  config.eager_load = false
  config.consider_all_requests_local = true

  if Rails.root.join('tmp/caching-dev.txt').exist?
    config.action_controller.perform_caching = true
    config.cache_store = :memory_store
    config.public_file_server.headers = {
      'Cache-Control' => "public, max-age=#{2.days.seconds.to_i}"
    }
  else
    config.action_controller.perform_caching = false
    config.cache_store = :null_store
  end

  config.action_mailer.raise_delivery_errors = true
  config.action_mailer.delivery_method = :test
  host = '**************.vfs.cloud9.us-east-2.amazonaws.com'
  config.action_mailer.default_url_options = { host: host, protocol: 'https' }
  config.action_mailer.perform_caching = false
  config.active_support.deprecation = :log
  config.active_record.migration_error = :page_load
  config.assets.debug = true
  config.assets.quiet = true
  config.file_watcher = ActiveSupport::EventedFileUpdateChecker
end

views/users/show.html.erb

<% provide(:title, @user.name) %>
<div class="row">
  <aside class="col-md-4">
    <section class="user_info">
      <h1>
        <%= gravatar_for @user %>
        <%= @user.name %>
      </h1>
    </section>
  </aside>
  <div class="col-md-8">
    <% if @user.microposts.any? %>
      <h3>Microposts (<%= @user.microposts.count %>)</h3>
      <ol class="microposts">
        <%= render @microposts %>
      </ol>
      <%= will_paginate @microposts %>
    <% end %>
  </div>
</div>

views/microposts/_micropost.html.erb

<li id="micropost-<%= micropost.id %>">
  <%= link_to gravatar_for(micropost.user, size: 50), micropost.user %>
  <span class="user"><%= link_to micropost.user.name, micropost.user %></span>
  <span class="content"><%= micropost.content %></span>
  <span class="timestamp">
    Posted <%= time_ago_in_words(micropost.created_at) %> ago.
  </span>
</li>

helpers/users_helper.rb

module UsersHelper
  
  #引数で与えられたユーザーのGravatar画像を返す
  def gravatar_for(user, size: 80)
    gravatar_id = Digest::MD5::hexdigest(user.email.downcase)
    size = url_options[:size]
    gravatar_url = "https://secure.gravatar.com/avatar/#{gravatar_id}?s=#{size}"
    image_tag(gravatar_url, alt: user.name, class: "gravatar")
  end
end