Changing Header Background Image on Internal Pages

Hello,

I am having no success changing the header background image on the internal pages of the Road Fighter theme (free version). I’m using the Custom CSS feature in my GoDaddy managed WordPress. I want to change it from the current dark gray gradient to just. plain. white.

My site is https://wpw3beta.info

When I use Inspect Element, it looks like one or both of these CSS statements are controlling that element:

.header_container.not_home{
    background:#2f2f2f url(images/header-bg.png) repeat-y;
    min-height:250px;
    border-bottom:1px solid #686869;
}
.page_index_container{
    background:#2f2f2f url(images/header-bg.png) repeat-y;
    min-height:195px;
    border-bottom:1px solid #686869;
}

In addition to going out on the server and changing the header-bg.png image from the gray gradient to a plain white bar (I know, not the best solution, but I’m really frustrated), I put the following into the Custom CSS:

.header_container.not_home{
    background:#fff url(images/header-bg.png) repeat-y;
}
.page_index_container{
    background:#fff url(images/header-bg.png) repeat-y;
}

And yet, in all browsers, the gray gradient is still displaying. How is that possible?