It’s actually the “line-height” that needs to be increased a little bit. Take a look around line 1165 in your css and change the line-height from 1.2 to 1.3 (or more if you want) –
h1,
h2,
h3,
h4,
h5,
h6,
.entry-title a {
line-height: 1.3;
margin-bottom: 16px;
margin-bottom: 1rem;
}