What is the method for applying a curved radius common border effect to the boundaries of two adjacent sections using CSS?

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One method for applying a curved radius common border effect to the boundaries of two adjacent sections using CSS is to use the "border-radius" property.

Here's an example:

.section {
  border: 1px solid black;
  border-radius: 10px; /* adjust value accordingly */
}

.section + .section {
  border-top: none;
  border-radius: 0 0 10px 10px; /* adjust value accordingly */
}

This CSS applies a 1px solid border to all sections and a border radius of 10px to all sections. For adjacent sections, the top border is removed and the border radius is changed to only apply to the bottom of the section. The values for the border radius can be adjusted to change the curvature and size of the effect.