It looks like your theme is adding a margin to the header class:
.entry-header {
margin-bottom: 24px;
margin-bottom: 1.714285714rem; /*<<<-this is an error buy the way */
}
Change it to:
.entry-header {
margin-bottom: 0;
}
Then add the margin to your header instead for where you are showing it:
h1.entry-title {
margin-bottom: 24px;
}