Please add this function to your MyHome Child Theme functions.php file with your custom CSS code (the one below example will change size heading 1 font size to 100px):

function admin_style() {
 echo '
 <style>
h1 {
 font-size:100px!important;
}
 </style>
 ';
}
 
add_action( 'admin_head', 'admin_style' );