The radius of the blur, specified as a <length>. It defines the value of the standard deviation to the Gaussian function, i.e., how many pixels on the screen blend into each other; thus, a larger value will create more blur. A value of 0 leaves the input unchanged. The lacuna value for interpolation is 0.
blur(0) /* No effect */
blur(8px) /* Blur with 8px radius */
blur(1.17rem) /* Blur with 1.17rem radius */