Change Mobile Font Size for Summary Block Title

Site URL: https://megalodon-jellyfish-ahzy.squarespace.com/

I have added in code already for the summary block so that the title displays on hover. The code has important tags for font size, which was placed to override the squarespace fonts. The size is fine on every site-width except for mobile. Is there a way that I can just change the mobile font size for summary block titles? 

Here is the code I've already put in:

/*the following code mimics the portfolio flatiron template with fade in rollover text*/

/* increase image transparency on hover */ 
  img.summary-thumbnail-image.loaded:hover 
  { 
  opacity: 0.4;
  }
/* display title on hover*/ 
  .sqs-block-summary-v2 .summary-item .summary-title 
  a{ 
  background-color: transparent; 
  opacity: 0; 
  color: #fff; 
    position: absolute;
     left: 0;
     right: 0;
     top: 45%;
     margin-left: auto;
      margin-right: auto;
 
 
  }

  .sqs-block-summary-v2 .summary-item:hover .summary-title 
  a{ 
  background-color: transparent; 
  opacity: 4; 
  color: #FFF; 
     position: absolute;
     left: 0;
     right: 0;
     top: 45%;
     margin-left: auto;
      margin-right: auto;
 
  }

/*style title font hover for summary wall block*/
.sqs-block-summary-v2 {
.summary-title,
.summary-heading {
font-family: 'FOUNDERSGROTESK'!important;
font-weight: 400 !important;
font-size: 30px !important;
color: #FFF;
 } 

}

/*eliminates white space between thumbnails*/
.summary-thumbnail-container,
.summary-title {
margin-bottom: 0 !important;
}

.summary-item
{background-color: #000000;}

@font-face {    
font-family: 'FOUNDERSGROTESK';       
src: url('https://static1.squarespace.com/static/5e8f3ac78b89c5205e278f15/t/5e96dd80faeb9808759ae30c/1586945408521/FoundersGrotesk-Light.otf');  }

h {font-family: 'FOUNDERSGROTESK';}
h1 {font-family: 'FOUNDERSGROTESK';}
h2 {font-family: 'FOUNDERSGROTESK';}
h3 {font-family: 'FOUNDERSGROTESK';}
h4 {font-family: 'FOUNDERSGROTESK';}
p {font-family: 'FOUNDERSGROTESK';}
p2 {font-family: 'FOUNDERSGROTESK';}
p3 {font-family: 'FOUNDERSGROTESK';}
p4 {font-family: 'FOUNDERSGROTESK';}

.blog-item-title h1.entry-title {
    font-family: FOUNDERSGROTESK !important;
}
.header-nav .header-nav-item a {
      font-family: 'FOUNDERSGROTESK';
}

.header-nav-folder-content .header-nav-folder-item a {
      font-family: 'FOUNDERSGROTESK';
}

.header-menu-nav-item a {
      font-family: 'FOUNDERSGROTESK';
}

.item-pagination h2.item-pagination-title {
      font-family: 'FOUNDERSGROTESK';
}
.sqs-block-button-element {
    font-family: 'FOUNDERSGROTESK';
      font-size: 20px !important;
    font-weight: 500 !important;
  height: 20px !important;
}

@media screen and (max-width:640px) {
nav.header-menu-nav-list {
    background: black;
}
}

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