CSS in border:1px solid rgba (0, 0, 0, 0.1); What is the meaning?

border:1px solid Rgba (0,0,0,0.1) means that the bounding rectangle of the set element is 1 pixels wide, the solid line, and the color is expressed using RGBA.
Where Rgba is an attribute in the CSS3,
The first 3 digits of the RGBA brackets represent the RGB values of red green blue Three colors, 0-255, and the last one is to set the transparency of this color, which is the alpha value. The range is from 0 to 1, and the closer it is to 1, the lower the transparency.

CSS in border:1px solid rgba (0, 0, 0, 0.1); What is the meaning?