Here's a Python definition of a del role, which works better than the accepted answer if you want to use the role in multiple pages of a Pelican blog or a Sphinx documentation project:

from docutils import nodes
from docutils.parsers.rst import roles

def deleted_role(_role, rawtext, text, _lineno, _inliner, options={}, _content=[]):
    roles.set_classes(options)
    options.setdefault('classes', []).append("del")
    return [nodes.inline(rawtext, text, **options)], []

roles.register_canonical_role('del', deleted_role)

Even better would be to extend the HTML writer to produce a proper <del> tag, like this:

from docutils import nodes
from docutils.parsers.rst import roles
from docutils.writers._html_base import HTMLTranslator

class delnode(nodes.inline):
    pass

def visit_delnode(self, node):
    self.body.append(self.starttag(node, 'del', ''))
def depart_delnode(self, node):
    self.body.append('</del>')

HTMLTranslator.visit_delnode = visit_delnode
HTMLTranslator.depart_delnode = depart_delnode

def deleted_role(_role, rawtext, text, _lineno, _inliner, options={}, _content=[]):
    roles.set_classes(options)
    return [delnode(rawtext, text, **options)], []

roles.register_canonical_role('del', deleted_role)

You can trivially adjust it to produce an <s>, of course.

Consider the user may have a different background, so here is no one solution that can be suitable for everyone.

1.Only one file

If you only use it only on one file. For example, you published a simple project to PyPI, and you may probably just only one README.rst file. The following may you want.

.. |ss| raw:: html

    <strike>

.. |se| raw:: html

    </strike>

single line
=============

|ss| abc\ |se|\defg

multiple line
=============

|ss|  
line 1

line 2
|se|

789

you can copy and paste it on this website: https://livesphinx.herokuapp.com/

and will see the picture as the following:

It's simple, and you can on directly see the preview on some IDE, for example, PyCharm.

bellow is writing for the users of Sphinx

2.beginner of Sphinx

If you are a beginner of Sphinx. ( I mean maybe you want to use Sphinx to create a document, but Python is not familiar for you ) then try as following:

# conf.py

from pathlib import Path
html_static_path = ['_static', ]
html_css_files = ['css/user.define.css']  # If you want to control which HTML should contain it, you can put it on the HTML, which is very like the answer by @Gregory Kuhn.

with open(Path(__file__).parent / Path('_static/css/user.define.rst'), 'r') as f:
    user_define_role = f.read()

rst_prolog = '\n'.join([ user_define_role + '\n',])  # will be included at the beginning of every source file that is read.
# rst_epilog = '\n'.join([ user_define_role + '\n',])  # it's ok if you put it on the end.

user.define.rst

.. role:: strike

user.define.css

.strike {text-decoration: line-through;}

With the rst_prolog, It can auto-add the role on each rst files, but if you change the content( that file, it contains a format that you define), then you must rebuild to make the render is correct.

3.Create roles

You can create an extension to achieve it.

# conf.py

extensions = ['_ext.rst_roles', ]
html_static_path = ['_static', ]
html_css_files = ['css/user.define.css']

# rst_roles.py
from sphinx.application import Sphinx
from docutils.parsers.rst import roles
from docutils import nodes
from docutils.parsers.rst.states import Inliner


def strike_role(role, rawtext, text, lineno, inliner: Inliner, options={}, content=[]):
    your_css_strike_name = 'strike'
    return nodes.inline(rawtext, text, **dict(classes=[your_css_strike_name])), []

def setup(app: Sphinx):
    roles.register_canonical_role('my-strike', strike_role)  # usage:  :my-strike:`content ...`

The full architecture:

• conf.py
• _ext/
  • rst_roles.py
• _static/
  • css/
    • user.define.css

about the rules, you can reference this link rst-roles

And I vary recommended you to see the docutils.parsers.rst.roles.py .

I wrote an extension for this.
Just pip install sphinxnotes-strike and use:

:strike:`text` 

or

:del:`text` 

to show strike text.

For more info: https://sphinx-notes.github.io/strike/

Since Docutils 0.17, the HTML5-writer uses <del> if a matching class value is found in inline, literal, or container elements:

.. role:: del

:del:`This text has been deleted`, here is the rest of the paragraph.

.. container:: del

  This paragraph has been deleted.