This can be done differently depending on the programming language that you used. For HTML, to create a table with a curved border, you simply need to add the following lines in the creation section of the table :
To be noticed that you can change the values as you like; this is only an example. Also, you can use other measurement types. If you plan on using another programming language to create your website, like CSS or C#, it's advised to visit the following website. You can find there a walkthrough about this matter.