An example of a module written in Sass.

_contact_form.scss

/* ===== Contact Form Styles ===== */

// Base styles
.contact_form {
    background: #FFF;
    border: 4px solid #999;
    padding: 10px;
}
.contact_form-label {
    color: #000;
    font-weight: bold;
}
.contact_form-styled_input {
    border: 1px solid #CCC;
    padding: 2px 4px;
}

// Mobile-only styles
@include mobile-only {
    .contact_form-label {
        display: block;
        font-size: 1em;
    }
    .contact_form-styled_input {
        display: block;
        font-size: 1em;
    }
}

// Desktop-only styles
@include desktop-only {
    .contact_form-label {
        display: inline-block;
        font-size: 1.2em;
    }
    .contact_form-styled_input {
        display: inline-block;
        font-size: 1.2em;
    }
}