Hi Vg,
To alter the height of your table rows, the two classes you want to take a look at are .sapUiTfBrd and .sapUiTableCtrl tr
If you're using Chrome, the below link may be helpful in explaining how to determine which SAPUI5 classes you need to add to your stylesheet in order to achieve the effect you are after.
https://developers.google.com/chrome-developer-tools/docs/elements-styles
Regards,
Ian