bootstrapのテンプレートをRailsに取り入れたい

皆様大変お忙しいと存じますが、お力添えいただけますと幸いです。

https://startbootstrap.com/themes/grayscale/

上記の"Grayscale"という綺麗なテンプレートを取り入れたいのですが、なかなか上手くいきません。

＜問題点＞
＊Javascriptが上手く動いていない（ページのジャンプ等）
＊一部適用されない画像がある

app/assets/stylesheets/application.scss

/*
 * This is a manifest file that'll be compiled into application.css, which will include all the files
 * listed below.
 *
 * Any CSS and SCSS file within this directory, lib/assets/stylesheets, or any plugin's
 * vendor/assets/stylesheets directory can be referenced here using a relative path.
 *
 * You're free to add application-wide styles to this file and they'll appear at the bottom of the
 * compiled file so the styles you add here take precedence over styles defined in any other CSS/SCSS
 * files in this directory. Styles in this file should be added after the last require_* statement.
 * It is generally better to create a new file per style scope.
 *
 */

 // Custom bootstrap variables must be set or imported *before* bootstrap.
 @import "bootstrap";

app/assets/javascripts/application.js

// This is a manifest file that'll be compiled into application.js, which will include all the files
// listed below.
//
// Any JavaScript/Coffee file within this directory, lib/assets/javascripts, or any plugin's
// vendor/assets/javascripts directory can be referenced here using a relative path.
//
// It's not advisable to add code directly here, but if you do, it'll appear at the bottom of the
// compiled file. JavaScript code in this file should be added after the last require_* statement.
//
// Read Sprockets README (https://github.com/rails/sprockets#sprockets-directives) for details
// about supported directives.
//
//= require rails-ujs
//= require activestorage
//= require jquery3
//= require popper
//= require bootstrap-sprockets
//= require_tree .

Gemfile

source 'https://rubygems.org'
git_source(:github) { |repo| "https://github.com/#{repo}.git" }

ruby '2.6.3'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '~> 5.2.3'
# Use sqlite3 as the database for Active Record
gem 'sqlite3'
# Use Puma as the app server
gem 'puma', '~> 3.11'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# See https://github.com/rails/execjs#readme for more supported runtimes
# gem 'mini_racer', platforms: :ruby

# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.2'
# Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
gem 'turbolinks', '~> 5'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.5'
# Use Redis adapter to run Action Cable in production
# gem 'redis', '~> 4.0'
# Use ActiveModel has_secure_password
# gem 'bcrypt', '~> 3.1.7'

# Use ActiveStorage variant
# gem 'mini_magick', '~> 4.8'

# Use Capistrano for deployment
# gem 'capistrano-rails', group: :development

# Reduces boot times through caching; required in config/boot.rb
gem 'bootsnap', '>= 1.1.0', require: false

group :development, :test do
  # Call 'byebug' anywhere in the code to stop execution and get a debugger console
  gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
end

group :development do
  # Access an interactive console on exception pages or by calling 'console' anywhere in the code.
  gem 'web-console', '>= 3.3.0'
  gem 'listen', '>= 3.0.5', '< 3.2'
  # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
  gem 'spring'
  gem 'spring-watcher-listen', '~> 2.0.0'
end

group :test do
  # Adds support for Capybara system testing and selenium driver
  gem 'capybara', '>= 2.15'
  gem 'selenium-webdriver'
  # Easy installation and use of chromedriver to run system tests with Chrome
  gem 'chromedriver-helper'
end

# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

gem 'bootstrap', '~> 4.3.1'
gem 'jquery-rails'