How can I change font family?

[sharonyue]

... only in this area and preview (not title and others)

.p
{
    font-family: Optima-Regular, "Times New Roman", serif;
}

Above does not work.

[baris]

You need to target the correct element, you can inspect the elements in your browser console to find the correct selectors.

For example

.composer .preview {
font-size: 24px;
color: green;
}

Will change the font-size and color of the composer.

[sharonyue]

@baris Thank you. How can I change this part's font? The following doesnot work.

.composer .p {
font-size: 24px;
color: green;
}

[baris]

That would be

.topic .content {

}

[sharonyue]

Thanks it works indeed!