公式サイト：https://getbootstrap.jp/docs/4.5/getting-started/introduction/
チートシート：https://hackerthemes.com/bootstrap-cheatsheet/
Bootstrap が用意しているスタイルですが、 Utilities で紹介されているスタイルは、特に important という指定が効いていて、他のクラスで上書きできなくなっている点に注意しておきましょう。
<!doctype html>
<html lang="ja">
<head>
<title>Hello, world!</title>
<!-- Required meta tags -->
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<!-- Bootstrap CSS -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.2/css/bootstrap.min.css" integrity="sha384-PsH8R72JQ3SOdhVi3uxftmaW6Vc51MKb0q5P2rRUpPvrszuE4W1povHYgTpBfshb" crossorigin="anonymous">
<style>
.box-container {
width: 100px;
height: 100px;
background: #ddd;
margin-bottom: 5px;
}
</style>
</head>
<body>
<!--
[p|m][location]-[size]
location:
- t, b, l, r
- x, y
size:
- 0
- 1: 0.25rem
- 2: 0.5rem
- 3: 1.0rem
- 4: 1.5rem
- 5: 3.0rem
- auto
-->
<div class="box-container">
<div class="bg-primary w-25 h-50 pt-3">BOX</div>
</div>
<div class="box-container">
<div class="bg-success w-75 h-100 my-0 mx-auto">BOX</div>
</div>
<div class="box-container">
<div class="bg-primary w-25 h-50">BOX</div>
</div>
<div class="box-container">
<div class="bg-success w-75 h-100">BOX</div>
</div>
<button class="btn btn-primary">OK</button>
<button class="btn btn-info btn-sm">OK</button>
<button class="btn btn-danger btn-lg">OK</button>
<h2 class="font-weight-normal display-4">Hello Bootstrap</h2>
<div class="text-center bg-primary">BOX</div>
<div class="text-right bg-success text-warning">BOX</div>
<div class="text-center bg-info font-weight-bold">BOX</div>
<div class="text-center bg-dark text-light">BOX</div>
<div class="container">
<div class="row">
<div class="col bg-primary">1</div>
<div class="col bg-secondary">2</div>
<div class="col bg-info">3</div>
</div>
<div class="row mb-3">
<div class="col bg-danger">1</div>
<div class="col bg-warning">2</div>
<div class="col bg-dark">3</div>
</div>
<div class="row">
<div class="col-8 bg-primary">1</div>
<div class="col-4 bg-secondary">2</div>
</div>
<div class="row mb-3">
<div class="col-4 bg-danger">1</div>
<div class="col-6 bg-warning">2</div>
<div class="col-2 bg-dark">3</div>
</div>
<div class="row">
<div class="col-8 bg-primary">1</div>
<div class="col-1 bg-secondary">2</div>
</div>
<div class="row mb-3">
<div class="col-4 bg-danger">1</div>
<div class="col-6 bg-warning">2</div>
<div class="col-6 bg-dark">3</div>
</div>
</div>
<!--ブレイクポイント
576px and up: sm
768px and up: md
992px and up: lg
1200px and up: xl
-->
<div class="container">
<div class="row">
<div class="col-10 bg-primary">1</div>
<div class="col-2 bg-secondary">2</div>
</div>
<div class="row">
<div class="col-10 col-md-2 bg-primary">1</div>
<div class="col-2 col-md-10 bg-secondary">2</div>
</div>
<div class="row">
<div class="col-10 bg-primary">1</div>
<div class="col-2 d-md-none bg-secondary">2</div>
</div>
<div class="row">
<div class="col-10 bg-primary">1</div>
<div class="d-none d-md-block col-md-2 bg-secondary">2</div>
</div>
</div>
<!-- Optional JavaScript -->
<!-- jQuery first, then Popper.js, then Bootstrap JS -->
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.3/umd/popper.min.js" integrity="sha384-vFJXuSJphROIrBnz7yo7oB41mKfc8JzQZiCq4NCceLEaO4IHwicKwpJf9c9IpFgh" crossorigin="anonymous"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.2/js/bootstrap.min.js" integrity="sha384-alpBpkh1PFOepccYVYDB4do5UnbKysX5WZXm3XxPqe5iKTfUKjNkCk9SaVuEZflJ" crossorigin="anonymous"></script>
</body>
</html>
<!doctype html>
<html lang="ja">
<head>
<title>Dotinstall App</title>
<!-- Required meta tags -->
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<!-- Bootstrap CSS -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.2/css/bootstrap.min.css" integrity="sha384-PsH8R72JQ3SOdhVi3uxftmaW6Vc51MKb0q5P2rRUpPvrszuE4W1povHYgTpBfshb" crossorigin="anonymous">
<style>
.cover {
background: url(img/bg.png);
background-size: cover;
}
</style>
</head>
<body>
<header>
<div class="alert alert-info text-center mb-0 rounded-0 alert-dismissible fade show">
News! News! News! News! News!
<button class="close" data-dismiss="alert">
×
</button>
</div>
<div class="container">
<nav class="navbar navbar-expand-sm navbar-light">
<a href="" class="navbar-brand">Logo</a>
<button class="navbar-toggler" data-toggle="collapse" data-target="#menu">
<span class="navbar-toggler-icon"></span>
</button>
<div id="menu" class="collapse navbar-collapse">
<ul class="navbar-nav">
<li class="nav-item"><a href="" class="nav-link">Link</a></li>
<li class="nav-item"><a href="" class="nav-link">Link</a></li>
<li class="nav-item"><a href="" class="nav-link">Link</a></li>
</ul>
</div>
</nav>
</div>
<div class="cover text-white text-center py-5">
<h1 class="display-4 mb-4">Dotinstall App</h1>
<a href="" class="btn btn-primary btn-lg">Get It Now!</a>
</div>
</header>
<main>
<section class="py-5">
<h2 class="text-center mb-5">Features</h2>
<div class="container">
<div class="mb-5 row">
<div class="col-sm-8">
<h3>Awesome</h3>
<p>Hello. Hello. Hello. Hello. Hello. Hello. Hello. Hello. Hello. Hello. Hello. Hello.</p>
</div>
<div class="col-sm-4">
<img src="img/phone.png" class="w-100 rounded-circle">
</div>
</div>
<div class="row">
<div class="col-sm-8 order-sm-2">
<h3>Awesome</h3>
<p>Hello. Hello. Hello. Hello. Hello. Hello. Hello. Hello. Hello. Hello. Hello. Hello.</p>
</div>
<div class="col-sm-4 order-sm-1">
<img src="img/movie.png" class="w-100 rounded-circle">
</div>
</div>
</div>
</section>
<section class="bg-light text-center py-5">
<h2 class="mb-5">Plans</h2>
<div class="container">
<table class="table table-hover">
<thead>
<tr><th>Plan A</th><th>Plan B</th></tr>
</thead>
<tbody>
<tr><td>AA</td><td>BB</td></tr>
<tr><td>AAA</td><td>BBB</td></tr>
<tr><td>AAAA</td><td>BBBB</td></tr>
</tbody>
</table>
</div>
</section>
<section class="py-5">
<h2 class="mb-5 text-center">How to use</h2>
<div class="container">
<ul class="nav nav-tabs">
<li class="nav-item"><a href="#ios" class="nav-link active" data-toggle="tab">iOS</a></li>
<li class="nav-item"><a href="#android" class="nav-link" data-toggle="tab">Android</a></li>
</ul>
<div class="tab-content py-4">
<div id="ios" class="tab-pane active">
<p>Hello iOS. Hello iOS. <span class="font-weight-bold text-info" data-toggle="tooltip" title="This is awesome" data-placement="bottom">Hello iOS. Hello iOS.</span> Hello iOS. Hello iOS. Hello iOS. Hello iOS. Hello iOS.</p>
</div>
<div id="android" class="tab-pane">
<p>Hello Android. Hello Android. Hello Android. Hello Android. Hello Android. Hello Android. Hello Android. Hello Android. Hello Android.</p>
</div>
</div>
</div>
</section>
<section class="bg-light text-center py-5">
<a href="" class="btn btn-primary btn-lg">Get It Now!</a>
</section>
</main>
<footer class="text-center text-muted py-4">
Copyright YYYY dotinstall.com
</footer>
<!-- Optional JavaScript -->
<!-- jQuery first, then Popper.js, then Bootstrap JS -->
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.3/umd/popper.min.js" integrity="sha384-vFJXuSJphROIrBnz7yo7oB41mKfc8JzQZiCq4NCceLEaO4IHwicKwpJf9c9IpFgh" crossorigin="anonymous"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.2/js/bootstrap.min.js" integrity="sha384-alpBpkh1PFOepccYVYDB4do5UnbKysX5WZXm3XxPqe5iKTfUKjNkCk9SaVuEZflJ" crossorigin="anonymous"></script>
<script>
$(function() {
'use strict';
$('[data-toggle="tooltip"]').tooltip();
});
</script>
</body>
</html>
デモ：http://samples.dotinstall.com/s/basic_twitter_bootstrap_v5/43022/MyBootstrap/index.html