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HTML

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HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

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Adding Classes

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About the <head>

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. If you need things in the <head> of the document, put that code here.

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Insecure Resource

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

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JavaScript

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JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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HTML 

              
                <html lang="en">
<head>


</head>
<body>

<!-- Page content-->
<div class="container mt-5">
	<div class="row">
		<div class="post-body col-lg-8">
			<!-- Post content-->
			<article>
			<!-- Post header-->
			<header class="mb-4">
			<!-- Post title-->
			<h1 class="fw-bolder mb-1">Welcome to Blog Post!</h1>
			<!-- Post meta content-->
			<div class="text-muted fst-italic mb-2">Posted on May 18, 2023 by Start Bootstrap</div>

			</header>
			<!-- Preview image figure-->
			<figure class="mb-4"><img class="img-fluid rounded" src="https://dummyimage.com/900x400/ced4da/6c757d.jpg" alt="..."/></figure>
			<!-- Post content-->
			<section class="mb-5">
<h2 class="fw-bolder mb-4 mt-5">Bootstrap heading</h2>
 <div class="alert alert-success" role="alert">
  This is a success alert—check it out!
</div>
			<p class="fs-5 mb-4">
				Science is an enterprise that should be cherished as an activity of the free human mind. Because it transforms who we are, how we live, and it gives us an understanding of our place in the universe.
			</p>
			<p class="fs-5 mb-4">
				The universe is large and old, and the ingredients for life as we know it are everywhere, so there's no reason to think that Earth would be unique in that regard. Whether of not the life became intelligent is a different question, and we'll see if we find that.
			</p>
			<p class="fs-5 mb-4">
				If you get asteroids about a kilometer in size, those are large enough and carry enough energy into our system to disrupt transportation, communication, the food chains, and that can be a really bad day on Earth.
			</p>
			<h2 class="fw-bolder mb-4 mt-5">I have odd cosmic thoughts every day</h2>
			<p class="fs-5 mb-4">
				For me, the most fascinating interface is Twitter. I have odd cosmic thoughts every day and I realized I could hold them to myself or share them with people who might be interested.
			</p>
			<p class="fs-5 mb-4">
				Venus has a runaway greenhouse effect. I kind of want to know what happened there because we're twirling knobs here on Earth without knowing the consequences of it. Mars once had running water. It's bone dry today. Something bad happened there as well.
			</p>
        
			<h3 class="fw-bolder mb-4 mt-5">Bootstrap Heading Fun</h3>
			<p class="fs-5 mb-4">
				For me, the most fascinating interface is Twitter. I have odd cosmic thoughts every day and I realized I could hold them to myself or share them with people who might be interested.
			</p>
			<p class="fs-5 mb-4">
				Venus has a runaway greenhouse effect. I kind of want to know what happened there because we're twirling knobs here on Earth without knowing the consequences of it. Mars once had running water. It's bone dry today. Something bad happened there as well.
			</p>

  			<h2 class="fw-bolder mb-4 mt-5">I have odd cosmic thoughts</h2>
			<p class="fs-5 mb-4">
				For me, the most fascinating interface is Twitter. I have odd cosmic thoughts every day and I realized I could hold them to myself or share them with people who might be interested.
			</p>
			<p class="fs-5 mb-4">
				Venus has a runaway greenhouse effect. I kind of want to know what happened there because we're twirling knobs here on Earth without knowing the consequences of it. Mars once had running water. It's bone dry today. Something bad happened there as well.
			</p>      
			</section>
			</article>
			<!-- Comments section-->
			<section class="mb-5">
			<div class="card bg-light">
				<div class="card-body">
					<!-- Comment form-->
					<form class="mb-4">
						<textarea class="form-control" rows="3" placeholder="Join the discussion and leave a comment!"></textarea>
					</form>
					<!-- Comment with nested comments-->
					<div class="d-flex mb-4">
						<!-- Parent comment-->
						<div class="flex-shrink-0">
							<img class="rounded-circle" src="https://dummyimage.com/50x50/ced4da/6c757d.jpg" alt="..."/>
						</div>
						<div class="ms-3">
							<div class="fw-bold">Commenter Name</div>
							 If you're going to lead a space frontier, it has to be government; it'll never be private enterprise. Because the space frontier is dangerous, and it's expensive, and it has unquantified risks. 
							<!-- Child comment 1-->
							<div class="d-flex mt-4">
								<div class="flex-shrink-0">
									<img class="rounded-circle" src="https://dummyimage.com/50x50/ced4da/6c757d.jpg" alt="..."/>
								</div>
								<div class="ms-3">
									<div class="fw-bold">Commenter Name</div>
									 And under those conditions, you cannot establish a capital-market evaluation of that enterprise. You can't get investors.
								</div>
							</div>
							<!-- Child comment 2-->
							<div class="d-flex mt-4">
								<div class="flex-shrink-0">
									<img class="rounded-circle" src="https://dummyimage.com/50x50/ced4da/6c757d.jpg" alt="..."/>
								</div>
								<div class="ms-3">
									<div class="fw-bold">Commenter Name</div>
									 When you put money directly to a problem, it makes a good headline.
								</div>
							</div>
						</div>
					</div>
					<!-- Single comment-->
					<div class="d-flex">
						<div class="flex-shrink-0">
							<img class="rounded-circle" src="https://dummyimage.com/50x50/ced4da/6c757d.jpg" alt="..."/>
						</div>
						<div class="ms-3">
							<div class="fw-bold">Commenter Name</div>
							 When I look at the universe and all the ways the universe wants to kill us, I find it hard to reconcile that with statements of beneficence.
						</div>
					</div>
				</div>
			</div>
			</section>
		</div>
		<!-- Side widgets-->
		<div class="col-lg-4">
			<!-- Search widget-->
			<div class="card mb-4">

				<div class="card-body">
					<div class="input-group">
						<input class="form-control" type="text" placeholder="Enter search term..." aria-label="Enter search term..." aria-describedby="button-search"/>
						<button class="btn btn-primary" id="button-search" type="button">Go!</button>
					</div>
				</div>
			</div>
			<!-- Table Of Content-->
			<div class="sticky-top card mb-4">
				<div class="card-body">
 <h4 class="card-title">Table of Content</h4>
					<div class="docs-toc scroll">
            <div class="Toc">
            <!-- Output Table Of Content-->
            </div>
          </div>
				</div>
			</div>
		</div>
	</div>
</div>

</body>
</html>
!

CSS 

              
                .toc-list{width:100%;position:relative;box-shadow:2px 0 0 0 #0000001a inset}.toc-list.is-collapsible .toc-link{padding-left:2.25rem}.toc-list.is-collapsed{display:none}.toc-link{display:block;color:#495057;padding:.75rem 1rem .75rem 1.5rem;transition:.5s}.toc-link.is-active-link{background-color:#eceff1;font-weight:500;box-shadow:2px 0 0 0 #495057 inset}.docs-toc{--bg-scrollbar-thumb:#ced4da;--bg-scrollbar-track:transparent}
@media (min-width:992px){.docs-toc .scroll{max-height:calc(100vh - 3.5rem - 44px)}}

ol.toc-list, ul.toc-list{list-style:none;padding:0;}
!

JS 

              
                var content=document.querySelector(".post-body"),headings=content.querySelectorAll("h2, h3, h4, h5, h6, h7"),headingMap={};Array.prototype.forEach.call(headings,function(e){var t=e.id?e.id:e.textContent.toLowerCase().replace(/[^a-z -]/gi,"").trim().split(" ").join("-").replace(/--/g,"-");headingMap[t]=isNaN(headingMap[t])?0:++headingMap[t],headingMap[t]?e.id=t+"-"+headingMap[t]:e.id=t}),tocbot.init({tocSelector:".Toc",contentSelector:".post-body",headingSelector:"h2, h3, h4, h5, h6, h7",hasInnerContainers:!0,listItemClass:"toc-list-item",orderedList:!1,headingsOffset:1});
!
999px

Console