Help please with mobile view

Site URL: https://www.exaltedmktg.co.uk/

Hi there

i have developed my site using the Mojave template. The fonts seem ok on laptop and tablet view but on mobile view my fonts are not aligning. 
Having contacted customer care they have suggested I could consider a workaround using custom code but I have no idea how to do this, is someone able to help?

Go to Design > Custom CSS and add the following (you can customize the font sizes to whatever works best with your design:

/*Reducing font size for screens smaller than 640px*/
@media screen and (max-width: 640px) {
  h1 {
    font-size: 33px;
  }}
@media screen and (max-width: 640px) {
  h2 {
    font-size: 26px;
  }}
@media screen and (max-width: 640px) {
  h3 {
    font-size: 20px;
  }}
@media screen and (max-width: 640px) {
  .blog-item-wrapper .blog-item-title h1.entry-title  {
    font-size: 24px;
  }}