Menu font changes with CSS addditon

Hi

on this under development site
https://aussiehiddentreasures.com/
front end password = aussie

When I try to add this css

@media only screen and (max-width: 600px) {
.single-product-summary {
width: 100%;
}

the menu font changes from bold green letters set in the admin – to thin black lettering

FYI the css above makes the woocommerce description the full width of the phone page (overriding the css to get the menu to the right on a normal size page)

here is the full custom css

.page-thumb { display: none;
}
.woocommerce-tabs { display: none !important;
}
.related.products {  display: none;
}
.template-shop {
    background-image: url(https://aussiehiddentreasures.com/wp-content/uploads/2020/01/bg5-light.jpg);
    background-repeat: repeat;
    background-position: top left;
}
.single-product .template-shop {
    background-image: url(https://aussiehiddentreasures.com/wp-content/uploads/2020/01/bg1.jpg);
    background-repeat: repeat;
    background-position: top left;
}
.single-product-summary  {
      background-image: url(https://aussiehiddentreasures.com/wp-content/uploads/2020/01/80-white-frost-panel-1.png);
    background-repeat: repeat;
padding-top: 20px;
  padding-right: 20px;
  padding-bottom: 20px;
  padding-left: 20px;
}
.inner_sidebar {
      background-image: url(https://aussiehiddentreasures.com/wp-content/uploads/2020/01/80-white-frost-panel-1.png);
    background-repeat: repeat;
padding-top: 20px;
  padding-right: 20px;
  padding-bottom: 20px;
  padding-left: 20px;
}
.pagination {
      background-image: url(https://aussiehiddentreasures.com/wp-content/uploads/2020/01/80-white-frost-panel-1.png);
    background-repeat: repeat;
padding-top: 20px;
  padding-right: 20px;
  padding-bottom: 20px;
  padding-left: 20px;
}
.single-product-main-image {
    width: 25%;
}
.single-product-summary {
    overflow: hidden;
    width: 45%;
    float: left;
    margin-right: 5%;
}
.single-product .sidebar {
    width: 30%;
}
@media only screen and (max-width: 600px) {
.single-product-summary {
width: 100%;
}