Can we change the font size of the message "This workflow task applies to" that is above the app

Hi,

You could add the code below to master page via SharePoint Designer 2013.

<style type="text/css">
.ms-informationbar
{
         font-size:20px !important;
}
</style>

About how to edit master page via SharePoint Designer 2013:

The result is shown as below:

Thanks,

Dean Wang

Does this affect all pages? I just wanted to change the message above the approval form?

Hi,

It would affect pages which contain ms-informationbar class. You could find WrkTaskIP.aspx page in All Files tab via SharePoint Designer 2013, then add the code in the page.

Thanks,

Dean Wang