That replacement CSS worked, thank you very much indeed.
The mobile menu toggle issue ended up being a server delay, meaning I couldn’t see the changes I’d made – the menu is now displaying as I want it to.
Thanks very much again for your assistance.
I assumed that’s where I’d make the change, but my color settings are restricted to changing the background (this is what I see – https://ibb.co/b27ghDM)
The color I want is #f8d210 – I’ve managed to alter the hover colour of the footer expand toggle but in doing so, the triangle has changed to a square. Similarly, I’ve been able to alter the colour of the central element of the menu toggle, but there’s still an outline on either side in the default theme red that I can’t get rid of.