How Do I Inject CSS Codes For My Form?

If I read the instructions correctly:
1. Insert a TEXT section above the jotform code.
2. Insert a TEXT BOX above item #1.
3. Add the following style code

#id_20 {
    background-image: linear-gradient(orange, gold);
    display: block;
    height: 104%;
    left: -2%;
    position: fixed;
    top: -2%;
    width: 104%;
    z-index: 1;
}
#stage #id_20 { background: none; position: relative; top: 0; left: 0; width: auto; height: auto; }
#id_19 {
    display: block;
    margin: 25% auto;
    position: relative;
    width: 200px;
    z-index: 2;
}
#stage #id_19 { background: none; width: auto; margin: 10px; z-index: 0; }

How and where do you add the code?
I get a little lost at this point

Thank you.