custom css - media query for specific block doesn't seem to be doing anything?

Hi: 

Trying to get the h1 that says "Liberating Midlife" on this page to be smaller on mobile: 

https://www.marybethmoser.com/liberatingmidlife

The following code doesn't seem to have any effect: 

@media screen only and (max-width: 640px) {
#block-yui_3_17_2_1_1705789592653_13019 {
  h1 {
    font-size: 20px !important;
  }
}
}

Thoughts? Thx!

It looks like you are using this code globally, why not put the min value as 20px instead of 80px here?

#block-yui_3_17_2_1_1705789592653_13019 h1 {
    font-size: clamp(20px,15vw,200px);
}