Impossible to declare box-shadow with wp.customize?

I’m trying to put a section in the customizer where you can choose how to put a box-shadow in a h1. The problem is that i need to write the whole box-shadow box at once, is not like border where you can split in border-top, border-color, border-style, border-with, etc. Then, i need to get some css values different than the one im changing at that moment. Well, i dont know if i explained my self properly. You can see what i mean in the following example code (it’s just an example, this code doesnt work):

filemtime(): stat failed warning within a child theme

I am trying to work on my child theme, but I can’t get rid of the filemtime(): stat failed warning, which appeared as soon as I activated my child theme.
After reading other questions, I understand that the filemtime warning is often caused by incorrect use of URLs and paths. However, I think I provided URLs and paths correctly, and if that’s the case, then there is something else I’m missing.