Dark mode for Sphinx ReadTheDocs theme

rtd_dark.css

/*!
 * @name          Readthedocs
 * @namespace     http://userstyles.org
 * @description	  Styles the documentation pages hosted on Readthedocs.io
 * @author        Anthony Post
 * @homepage      https://userstyles.org/styles/142968
 * @version       0.20170529055029
 *
 * Modified by Aloïs Dreyfus: 20200527-1037
 * Modified by Erik Kalkoken: 20220615
 */

@media (prefers-color-scheme: dark) {
	a:visited {
		color: #bf84d8;
	}

	pre {
		background-color: #2d2d2d !important;
	}

	.wy-nav-content {
		background: #3c3c3c;
		color: aliceblue;
	}

	.method dt, .class dt, .data dt, .attribute dt, .function dt,
	.descclassname, .descname {
		background-color: #525252 !important;
		color: white !important;
	}

	.toc-backref {
		color: grey !important;
	}

	code.literal {
		background-color: #2d2d2d !important;
		border: 1px solid #6d6d6d !important;
	}

	.wy-nav-content-wrap {
		background-color: rgba(0, 0, 0, 0.6) !important;
	}

	.sidebar {
		background-color: #191919 !important;
	}

	.sidebar-title {
		background-color: #2b2b2b !important;
	}

	.xref, .py-meth {
		color: #7ec3e6 !important;
	}

	.admonition, .note {
		background-color: #2d2d2d !important;
	}

	.wy-side-nav-search {
		background-color: inherit;
		border-bottom: 1px solid #fcfcfc;
	}

	.wy-table thead, .rst-content table.docutils thead, .rst-content table.field-list thead {
		background-color: #b9b9b9;
	}

	.wy-table thead th, .rst-content table.docutils thead th, .rst-content table.field-list thead th {
		border: solid 2px #e1e4e5;
	}

	.wy-table thead p, .rst-content table.docutils thead p, .rst-content table.field-list thead p {
		margin: 0;
	}

	.wy-table-odd td, .wy-table-striped tr:nth-child(2n-1) td, .rst-content table.docutils:not(.field-list) tr:nth-child(2n-1) td {
		background-color: #343131;
	}

	.highlight .m {
		color: inherit
	}

	/* Literal.Number */
	.highlight .nv {
		color: #3a7ca8
	}

	/* Name.Variable */

	body {
		text-align: justify;
	}

	.rst-content .section .admonition ul {
		margin-bottom: 0;
	}

	li.toctree-l1 {
		margin-top: 5px;
		margin-bottom: 5px;
	}

	.wy-menu-vertical li code {
		color: #E74C3C;
	}

	.wy-menu-vertical .xref {
		color: #2980B9 !important;
	}
}

html_css_files = [
    'css/rtd_dark.css',
]

@ErikKalkoken Where should l create the /css folder?
And how to enable the dark mode?

How to change the theme automatically?

@ErikKalkoken

@mendax1234 Hey, I update the description to make the folder structure more clear.

Thanks!