can you share your URL, please?

Thanks I have sent in private becouse the site is still in development

Did you do any CSS changes? 

Because here's how the element should look in the default theme

and you don't have this background image element in the styles at all

Yes, could be. I have a strange behaviour. If I use the CSS editor of admin, it occures that the editor create a new custmo base.css file which is not complete. I mean it will save not every row of the file (e.g. 150 lines instead of 200 lines).
So, ok it is the css. I have to compare the oroginal base.css to the new one.
Anyways...
Isn't it strange that the editor will save just a part of the content I paste in it? Im' using FTP to avoid using the css editor and have my css file trunk. Thanks!

Ok thank you for help.
The problem occured becouse the embedded CSS editor, will not save all the lines of the CSS file. This is very strange. The file is cut much before than the end of the code. So that's why my css code was incomple/corrupted.
Do you have any suggestion why this occures?

I saw that you have copied the styles shown in the theme customizer and copied to the edit area and applied your styles there as well, no need to copy current content, just apply your styles. 

Do not do the changes in the base.css or in the files, as these changes will be overwritten while next update of the software. 

Ok. You have been very helpful. It still remains the problem in the editor of the customizer. It will only save part of the css file. I don't care of it, I will use FTP instead. Thank you for help!

Revert the changes or replace the current base.css file with the original one and apply your changes in the theme customer this will get your icons back

Yes, done thanks, solved!

Great