If a value is used
Taking a value will take four sides of the div.
If two value is used
Given two values of the border-radius of a div, the first will take the upper left side and the lower right side of the div, while the second will take the upper right side and the lower left side of the div.
If three value is used
If three values are taken, the first one will be the upper left side of the div, the second the upper right side and the lower left, the third will take the lower right side of the div.
If four value is used
If you take four values, the first one will be the upper left, the second the upper left, the third lower right and the last one the lower left.