How can I use tables to structure forms?

Small forms are sometimes placed within a TD element within a table. This can be a useful for positioning a form relative to other content, but it doesn't help position the form-related elements relative to each other. To position form-related elements relative to each other, the entire table must be within the form. You cannot start a form in one TH or TD element and end in another. You cannot place the form within the table without placing it inside a TH or TD element. You can put the table inside the form, and then use the table to position the INPUT, TEXTAREA, SELECT, and other form-related elements, as shown in the following example.

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How do I center a table?
In your HTML, use

...

In your CSS, use div
.center
{ text-align: center;

}
div.center table
{
margin-left: auto; margin-right: auto; text-align: left;
}