Box shadow is CSS effect used in web developed and web designing in css (Cascading Style Sheets) file or html inline code. Shaodw gives an elment div a floating effect behind of element on a webpage.

Horizontal offset: Horitzontal distance the shadow should be offset from element.

Vertical offset: Horitzontal distance the shadow should be offset from element.

Blur radius: Its amount of blur applied to the shadow on element.

Spread radius: Its amount of spread applied to the shadow on element.

Color: Specifies the color of the shadow

                        .box {
                              width: 100px;
                              height: 100px;
                              background-color: #FF0000;
                              box-shadow: 5px 5px 10px rgba(0, 0, 0, 0.65);
                            }
                                

In this example, a red box with a shadow is created. The box is offset 5 pixels to the right and 5 pixels down, has a blur radius of 10 pixels, and uses a semi-transparent black shadow color.