how to assign the height as the width in % in css code example

Example: css image size adjust

squareImage {
  border: 1px solid #ddd;	/* thickness and color of border */
  border-radius: 4px;		/* edge rounding of border */
  width: 150px;				/* width of image (px or % or auto) */
  height: auto;				/* height of image (px or % or auto) */
}