Creating additional styles for the template

Hi. I have created an additional style for my template which the end user can select using a dropdown box, but am having a small issue with the necessary code to select it.
The code in the index.php is php (d'uh'), and I have no idea how to code for this.

So far, the code I am using is just modified from the default index.php where it chooses template.css or template_rtl.css.

original code:

I have modified this to:

and I have created a dropdown selector box in the template advanced parameters with:

This is inserted into the templateDetails.xml file.

All is working fine and I can select the second style sheet (dark.css) and it is applied correctly to the site.

What I would like to know is how I can utilise this function with the template_rtl.css?
As it stands, the 'dark.css' can only be used if the site is not RTL.
How can I word the coding so that it can use 'dark_rtl.css' if dark is chosen and the site is RTL?
I could do this by removing the if > else statement and just adding template_rtl.css and dark_rtl.css to the dropdown, but the user would have to select the correct style if they used rtl, and I would like to eliminate that.

I know this is WAAAAY outside the remit for any support, but would just like a few pointers as to how to get this working correctly.

Would be amazing if you could add the ability to add different styles within template creator, but I realise this is probably a LOT of work.

Hi
this is a very specific request and needs some PHP skills.
I would do that
1/ in the options, use
<option value="dark">Dark</option>
(without .css)
2/ in the php
CEd

man, thats sooooo simple. I feel like an idiot for not figuring that one out myself.

But now I have the ability for the end-user to select different styles. Thanks very much for the quick pointer