Please find code here :-

1. Create XML file to Override the Orderline template to add an attribute
<?xml version="1.0" encoding="UTF-8"?>
<templates id="template" xml:space="preserve">

<t t-name="Orderline" t-inherit="point_of_sale.Orderline" t-inherit-mode="extension" owl="1">
<xpath expr="//li[hasclass('orderline')]" position="attributes">
<attribute name="t-attf-style">{{props.line.get_display_price() - props.line.get_total_cost() lt 0 ? 'color:red;': ''}}</attribute>
</xpath>
</t>

</templates>

2. Add point_of_sale in depends and Register your XML in __manifest__.py file
'depends': ['point_of_sale'],
'assets': {
'point_of_sale.assets': [
'module_name/path/to/your/file.xml',
],
},