PR: Fix error in link to css files (Online Help)

[Virinas-code]

Description of Changes

• Wrote at least one-line docstrings (for any new functions)
• Added unit test(s) covering the changes (if testable)
• Included a screenshot or animation (if affecting the UI, see Licecap)

Just use a absolute URL for style sheets.
Can't test new code because of dependencies problems.

Issue(s) Resolved

Fixes #15847

Affirmation

By submitting this Pull Request or typing my (user)name below,
I affirm the Developer Certificate of Origin
with respect to all commits and content included in this PR,
and understand I am releasing the same under Spyder's MIT (Expat) license.

I certify the above statement is true and correct:
@Virinas-code

[ccordoba12]

Hey @Virinas-code, thanks a lot for your help! Did you test this change by applying it to the current Spyder installation?

[Virinas-code]

I can't test it because i've got dependencies problems.

[ccordoba12]

Yeah, I read that part in your first message. But do you have problems with running Spyder from git? Or with your locally installed Spyder?

[Virinas-code]

Yeah, I read that part in your first message. But do you have problems with running Spyder from git? Or with your locally installed Spyder?

When I use git it can't install pyflakes version.
I use pip for my spyder.

[Virinas-code]

error: pycodestyle 2.6.0 is installed but pycodestyle>=2.7.0 is required by {'autopep8'}

[Virinas-code]

But :

 root  /  opt  spyder  pycodestyle --version
2.7.0
 root  /  opt  spyder  

[ccordoba12]

Ok, could apply the patch then to your installed Spyder to see if it works?

[Virinas-code]

Ok, could apply the patch then to your installed Spyder to see if it works?

I'm trying...

[Virinas-code]

Yes it fix bug !

[Virinas-code]

I've got the error without the patch, but no errors with the patch.

[ccordoba12]

Thanks a lot @Virinas-code for your contribution!

[ccordoba12]

This will be part of our 5.1.0 version, to be released at the end of July.