Frosted Glass Effect on transparent PNGs

Hi everyone,
I just started customizing my website and I’m having difficulties. keep in mind I’m a total noob when it comes to coding. I tried following this tutorial to make my logo, which is a transparent png, with a ‘frosted glass’ effect, but it doesn’t seem to work. it just creates either a blurred square or circle behind the logo, which is still white. Can anyone help me with this? Thank you so much !