How to change the Font size using 'Custom CSS' field

[Kmt2000]

Please suggest me how to change the font size using the Field i have shown in shared image? what will be the code for that?

[anat]

can u try below code:

element.style {
    font-size: 1.15385em;
    font-family: "QlikView Sans", sans-serif;
    color: rgb(128, 128, 128);
    padding-right: 0px;
    padding-left: 0px;
}