Missing navigation arrows on coloured themes

On a recent install, the navigation arrows and other functions on the coloured themes are missing, but they are present on the Xerte Online Toolkits theme and the Black & White theme. The functionality is there if I hover the mouse in the appropriate places for the arrows, hamburger menu, etc, just can't see the icons.
Any ideas?

Hi Peter

Check the theme folders to make sure the images are there (e.g. in themes/Nottingham/flatred there should be 11 different images for buttons)

The only difference I can see between the themes that are working for you and those that aren't is that the button images are .svg files in the ones that won't work and .png images where they are working. If the images are in the folders where they are supposed to be then perhaps it's a server issue with how these svg files are dealt with ( css-tricks.com/snippets/htaccess/serve-s...orrect-content-type/ )

Fay