Hello @iftekhermamun
Thanks for writing to us.
You are using default skin of WP Post tabs so you need to use classes of default skin.
You can apply Custom style CSS to WP Post Tabs. Put your Custom style in Settings => WP Post Tabs => Miscellaneous => Custom Styles and save changes.
You just need to use class of element and CSS properties with !important.
Example: .wordpress-post-tabs-skin-default .ui-tabs .ui-tabs-nav li{word-wrap: break-word !important;width: 150px !important;white-space: normal !important;}
Let me know if it helps.
Thank you,
Best Regards,
Ravi.