Antd: How to override style of a single instance of a component
You should target Tabs component with css by adding a custom css class / id. Then you can customize that class/id in your css file. In your specific case where you add .ipf-appbar class you can style that specific component as follows:
.ipf-appbar .ant-tabs-bar {
font-size: 24px; // this applies to all text in the Tabs component
border-bottom: 1px solid darkmagenta; // also applies to all border
}