Markdown css Just add <link href="style.css" rel="stylesheet"></link> to the start of your markdown document.

Antimony.css

* { margin: 0; padding: 0; }

abbr,acronym,blockquote,code,dir,kbd,listing,plaintext,q,samp,tt,var,xmp { hyphens: none; }

html {
  padding: 2em;
	
	font: normal 18px/1.25 Source Sans Pro, sans-serif;
	color: #000;
	hyphens: auto;
	word-wrap: break-word;
	
	background: #fff;
}

body > :first-child {
	margin-top: 0;
}

/* @group Headings */

h1,h2,h3,h4,h5,h6 {
	line-height: 1;
	margin: 0;
	margin-top: 1.5rem;
	text-rendering: optimizeLegibility;
}

h1 { font-size: 2.75rem; }
h2 { font-size: 2rem; }
h3 { font-size: 1.65rem; }
h4 { font-size: 1.25rem; }
h5 { font-size: 1.1rem; }
h6 { font-size: 1rem; }

h2 em, h3 em{
	color:grey;
}

/* @end */

small {
	font-size: 65%;
}

p {
	margin-top: .75rem;
}

hr {
	margin: .75rem 0;
	
	opacity: .5;
}

ol,ul {
	margin-top: .75rem;
}

ol ul, ol ol, ul ul, ul ol {
	margin-left: 2rem;
	margin-bottom: .75rem;
}

li {
	margin: .5em 0;
}

abbr {
	font-variant: small-caps;
	font-weight: 600;
	text-transform: lowercase;
	color: #808080;
}

abbr[title]:hover {
	cursor: help;
}

/* @group Block Quotes */

blockquote {
	border-left: 5px solid #333;
	padding-left: .75em;
	margin-left: calc(-.75em - 5px);
	
	font-style: italic;
}

blockquote + figcaption {
	display: block;
	
	margin-top: -1.5rem;
	margin-bottom: 1.5rem;
	
	font-size: 75%;
	text-align: right;
}

blockquote + figcaption:before {
	content: "— ";

	opacity: .05;
}

/* @end */

/* @group Pre-formatted and Code */

pre {
	overflow: auto;
	
	margin: .75rem 0;
	padding: .5rem;

	font-size: .875em;
	white-space: pre;
	
	background-color: #f8f8f8;
	border: 1px solid #ccc;
	border-radius: 3px;
}

code {
	padding: 0 .25em;
	
	white-space: pre;
	font-family: Source Code Pro, monospace;
	
	background-color: #f8f8f8;
	border: 1px solid #ccc;
	border-radius: 3px;
}

pre code {
	padding: 0;

	word-wrap: normal;
	white-space: pre-wrap;
}

pre code, pre tt {
	background-color: transparent;
	border: none;
}

/* @end */

/* @group Tables */

table {
	margin: .75rem 0;
	padding: 0;
	
	border-collapse: collapse;
}
table tr {
	margin: 0;
	padding: 0;
	
	border-top: 1px solid #ccc;
	background-color: #fff;
}
	table tr:nth-child(2n) {
		background-color: #f8f8f8;
	}

table tr th {
	margin: 0;
	padding: .35em .75em;
	
	font-weight: bold;
	text-align: left;
	
	border: 1px solid #ccc;
}

table tr td {
	margin: 0;
	padding: .35em .75em;
	
	text-align: left;
	
	border: 1px solid #ccc;
}

table tr th :first-child, table tr td :first-child { margin-top: 0; }
table tr th :last-child, table tr td :last-child { margin-bottom: 0; }

/* @end */

Nice stylesheet! I found your post here while searching for "import stylesheet in markdown file". Adding the <link> tag to the head of my markdown document as you prescribed,

<link href="style.css" rel="stylesheet"></link>

did not work, unfortunately. I had high hopes that this was the solution. But, the only thing that worked was adding the styles within paired <style> tags.

My Setup:

• IDE: VS Code
• Extension: Auto-Open Markdown Preview

UPDATE: (08/15/22)

Well, I take that back ... it DOES work! Apparently there is a lag issue between the preview updating from the external stylesheet. But, after troubleshooting a bit more I found that running CTRL + SHIFT + P and then Developer: Reload Window while having the markdown document focused does the trick. So a reload is required with the Auto-Open Markdown Preview plugin to make external styles take effect within markdown files, it seems.

Hopefully this info will help somebody else!

Glad it helped someone 8 years later! Completely forgot this was here!

It was really helpful, it works. Thanks

Where do you insert the tag if you are using hugo. My markdown starts with the metadata.

linkTitle: "Configuration Library"
title: "Configuration Library"
weight: "1"
aliases:
  - /en/configuration-library.html

@radhikapc I'd suggest searching online, this tutorial might help
https://hugo-mini-course.netlify.app/sections/styling/custom/

But it doesn't render in github profile.
Please help me~