Post background help?

[gallifrey_eire]

Hello! I don't know if this has been answered yet, I did a bit of looking but wasn't able to find it...

I'm looking to change the background color of my posts/the inner box area. The main page background is fine, I just want the inner portion to be black or dark grey, with white text. I love reading off my phone at night and I'm sure a lot of other people do as well, so I'm hoping changing my journal to a more "night mode" look would make reading a little easier.

I have a paid account, and I'm using Minimal Blue.

This is all the CSS I'm using right now, for the header and such:

html body {
padding: 10px 0 0 0;
margin-right: 0;
margin-left: 0;
}
/* dump the journal name */
#header-name, #header-description {
display: none;}
/* -------------------------------------------------------- */
/* ---------- ADD YOUR HEADER GRAPHIC BELOW --------------- */
/* -------------------------------------------------------- */
#header {position: relative; height: 360px; width: 1220px; background: url(http://i.imgur.com/fEonZ.png) top center no-repeat;}
#header-inner {
width: auto;
height: 370px;
}
#header-text {
position: relative;
top: 320px;
width: auto;
}
#header .nav, #header-name {
margin-bottom: 5px;
width: 1220px;
background: #000000;
}
/*
- make sure that your height is the height of your graphic plus 40px
- e.g. if your graphic is 350px, your height should be 390px
*/
/* -------------------------------------------------------- */
/* ---------- ADD YOUR HEADER GRAPHIC ABOVE --------------- */
/* -------------------------------------------------------- */

Thanks!