Hello,
I would like to create this bar on each side of the slideshow box in the header:
https://www.sarstedt.com/en/home/
Any tips on how to do this? Thanks!

You realize that this is a forum for the WordPress theme Atahualpa and you are not using the theme or WordPress. And in addition, you have been a member here since 2009, posted 59 times and never given a donation.

So, why are you asking this question here?

Thanks I have used this theme for all of my 4 sites in the last 6 years, most of the posts would be from the time one site got hacked and I asked for your help. I have considered donating but from your attitude I would reconsider.
The link sent was an example site where there are red bars across the top, which probably does not use the theme. If you are not willing to help then I will ask someone else. Thank you for leaving a sour taste in my mouth.

When you don't provide the url of your site - how are we suppose to guess what you want? If you take the time to go back and reread your original post

I would like to create this bar on each side of the slideshow box in the header:
https://www.sarstedt.com/en/home/
Any tips on how to do this? Thanks!

you might see that your post is confusing. You might have said something like

On my site (insert your url here) I'd like to add a red bar behing my slideshow box like they are doing in this non-wordpress site other site.com. I'm using the xxxx slideshow plugin.

These are the things I've tried already
list
of
things
you
tried

Have you even searched the forums for an answer?
Did you look thru the FAQ forum?
Have you done your basic homework and looked at the CSS that that site is using?
or are you hoping we will do that for you?