Write feature spec of modal
user
```ruby
require "spec_helper"

feature "About BigCo modal" do
  scenario "toggles display of the modal about display", js: true do
    visit root_path

    expect(page).to_not have_content "About BigCo"
    expect(page).to_not have_content "BigCo produces the finest widgets in all the land"

    click_link "About Us"

    expect(page).to have_content "About BigCo"
    expect(page).to have_content "BigCo produces the finest widgets in all the land"

    within "#about_us" do
      click_button "Close"
    end

    expect(page).to_not have_content "About BigCo"
    expect(page).to_not have_content "BigCo produces the finest widgets in all the land"
  end
end
```
assistant