Hi
Adding the given code with tools > edit custom css, has no effect.
I also tried:
.t4-masthead:before {
padding-left: 0px;
padding-right: 0px;
}
and
.t4-masthead .ja-masthead:before {
color: #fff;
position: relative;
background-repeat: no-repeat;
background-size: cover;
z-index: 0;
}
Seems the custom code does not overwrite the templates css.