Trying to put in some code, but scared to edit

So I was using wordpress for my site a few weeks back, and I had to shut down my site. It’s back now, and I downloaded my theme (syntax), and am looking on edit it a little.

Here’s the code I’m trying to implement:

.site-title {
font-family: “Courier New”, “Courier”, monospace;
}

and

.site-header {
background: #fff;
}
.site-title a {
color: #000;
}

In the version I was using, there was an option “edit CSS” but now that’s gone. What do I do?