addind rounded corners on twenty ten theme

You shouldn’t edit the theme’s files.

Install this Custom CSS Manager plugin and use its section of the dashboard to hold your CSS modifications.

That means creating new styles instead of modifying existing ones.

If you’re stuck on CSS, try this generator https://css3generator.com/ and select ‘Border Radius’ from the drop down menu.

i don’t understand how to use the plugin
cause it written the code from right to left instead of left to right
and y i can’t change the original code
tnxs
shiry
this is my web: [email protected]
i want to change the color of the wrapper
and the navigator bar color,font the the hover situation

and the drop down menu style

@shiry marcus noik
The reason why you should not edit the theme CSS is .
Next time when you update the wordpress chances are your theme gets updated and you will lose the changes.

thats why Andrew asked you to use the custom css manager to override the default CSS.
the another way to edit the template file is creating a child theme
Please refer the codex
https://codex.www.ads-software.com/Child_Themes