

I can see border CSS is working
.accordions-tab-head {border: 2px solid #ffffff;}
Please try to bellow to remove tabs nav icons
.accordions-tab-icons {
display: none !important;
}
Accordion and tab content: background, border also working
http://i.imgur.com/WpmI6vN.png
Accordion and tab content: Line height also working
Please try clean cache on your browser and refresh.
Regards

You can see the accordions and tabs on my test site.
http://test.pat.gen.nz/vertical-accordion/
http://test.pat.gen.nz/tabs/
At present I use the default colours for the accordion/tab headers. I would like to change them to the colours that I used with my plug-in which is no longer supported. I realise that I could set them for each individual accordion but, to give more flexibility, I would prefer to define the colours just once - in my child theme. I am not sure which classes (accordions-head, accordions-tab-head etc) I should refer to in the CSS.
Andy

Welcome to our forum,
Please feature "Header background color" only available in premium version.
http://i.imgur.com/wcWFQGf.png
Please see this screenshot where the option for icon color (also available in Free version)
http://i.imgur.com/0SbYiKb.png
Accordion content p tag css should used from your theme CSS although you can override by "!important"
Can you please send me your accordion page url ?
Regards