On this page, you’ll find information on creating an SVG drop shadow. For that purpose, you can use the SVG <feDropShadow> element or the CSS filter property.
To set a box shadow on one side of an element, use the box-shadow property. Read and find examples of adding box shadows outside and inside an element.
In this snippet, you can find some solutions to the problem of adding a box-shadow only on the left and right sides of the element. Use the box-shadow property.