css - How can I make this background image responsive? wordpress -

ok have custom wordpress theme , have tried multiple different ways work.

the issue i'm having on mobile screens , small screens crops image instead of rescaling fit screen.

i'm trying edit splash img here's code.

    .stockimage { /*background-image:url('../img/guitarpic.jpg');*/ background-image:url('../img/splash-2.png'); background-size:100% 100%; background-size:cover; background-position:center center;  } 

i've tried bootstrap etc no avail haven't got work of yet.

fixed issue removing background-size:cover; , replacing background-size: 100% 100%