Bootstrap it's a library. The library contains templates CSS, HTML, JavaScript, design for buttons, labels, tables, web forms and other elements web Pages.
Bootstrap uses the library
jQuery
Bootstrap Useful for mobile phones and devices with small screens. It comes with a library of buttons, navigation styles, and other reusable tools.
The most important thing,
Bootstrap makes it easier to work with different browsers and platforms.
Html
<html>
<!-- heading -->
<head>
<meta charset="utf-8">
<title>Example</title>
</head>
<!-- page -->
<body>
<!-- connect library jQuery -->
<script src="https://dir.by/example_lib/jquery/jquery-3.3.1.min.js"></script>
<!-- connect library Bootstrap (css file) -->
<link rel="stylesheet" href="https://dir.by/example_lib/bootstrap-4.1.3/css/bootstrap.min.css">
<!-- connect library Bootstrap (js file) -->
<script src="https://dir.by/example_lib/bootstrap-4.1.3/js/bootstrap.min.js"></script>
<!-- HTML Elements -->
<form>
<div class="form-group">
<label for="email">Email address:</label>
<input type="email" style='width:300px;' class="form-control" id="email">
</div>
<div class="form-group">
<label for="pwd">Password:</label>
<input type="password" style='width:300px;' class="form-control" id="pwd">
</div>
<div class="checkbox">
<label><input type="checkbox"> Remember me</label>
</div>
<button type="submit" class="btn btn-default">Submit</button>
</form>
</body>
</html>
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