Form With Borders and grids (Look and Feel)
you should modify css files in order to modify the appearance of all your widgets accross the application. There is also an option to modify the appearance of one specific widget in the Form builder, by selecting a widget and using Appearance tab.
Note that there is an existing functionality in Subscription edition, that might be interesting as it helps to save a lot of time and gives a possibilty to modify the Look and Feel more easily.
Thank you for your ans, i m using community version . so i have to modify CSS thanks again