One of the shortcomings of the Owl Carousel in the Helium template is the lack of classes in each individual slide. So I have added it to one of my sites and it works great.
Here is how to do it.
In the "templates\g5_helium\particles" folder, open the "owlcarousel.yaml" file and make this change. Below the 'buttonclass' add the 'slideclass' code.
.buttonclass:
type: input.text
label: Button Class
description: Input the button class.
default: 'button-outline'
.slideclass:
type: input.text
label: Slide Class
description: Input the slide class.
default: 'slide-container'
Once this is done, your slides should have a new field to add a slide class like the image below.
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In the "templates\g5_helium\particles" folder, open the "owlcarousel.html.twig" file and make this change.
ORIGINAL:
<div class="g-owlcarousel-item owl-item">
CHANGE:
<div class="g-owlcarousel-item owl-item {{ item.slideclass|e }}">
In your page, the slide class is displayed and you can style individual slides without having to use that dreaded 'nth-child' selector! 
As you can see, I styled this particular slide to pad the H1 and H2 by 50% to move the text to the right side of the slide while leaving the link and navigation dots centered as well as changing the font size of the header tags.
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Enjoy!
NOTE TO GANTRY DEVELOPERS: Add this to a future update of the Helium template!
The following users have thanked you: David Goode, Kat05, MrT, Matt, Damir