xhtml_style: fix invisible cursor in textarea with chrome
With chrome ( 85.0.4183.108 but I think it appears a few weeks/months ago ) when using erp5_xhtml_style when the cursor in the first column on the left it's not visible, because the bold background hides it.
Default user agent spreadsheet is a 2px padding, but we have a rule applying a padding 0 for all textarea. Revert this rule for textarea used as fields in content.
before:
The cursor is in Description field, left to "This style is ..." but cannot be seen.
after:
The cursor is same location (Description field, left to "This style is ...") and this time is visible.
