# change ordering of label+checkbox for standard forms
tt_content.mailform.20.CHECK.layout = <div class="csc-mailform-field-checkbox">###FIELD### ###LABEL###</div>

# change html output for required form markers. The following example places the asterisk at the end of the form field
tt_content.mailform.20.REQ.labelWrap.wrap=|*

# JavaScript popup error message for form fields
tt_content.mailform.20.badMess = Please fill out the following fields:


# own CSS class for every form field
tt_content.mailform.20 {
  commentWrap.cObject = COA
  commentWrap.cObject {
    20=TEXT
    20.value = field-{current:1}
    20.insertData=1
  }
  layout(
    <div class="csc-mailform-field ###COMMENT###">###LABEL### <span class="csc-mailform-label">###FIELD###</span></div>
  )
}

These are some basic TS settings for the standard forms module.

TypoScript basics for forms

TYPO3