Custom Scroll Box Code??? Help???

[iDesiSaurus]

help me with a scroll custom box code.

I looked up how to do it but none of these codes seem to be working :/

[Unknighted Yoshi]

#id_custom_(number) {
height: __px;
overflow-y: auto;
}

Hover the element in edit mode to see the ID apply the number.
Add the height that you want.