.edit-post-visual-editor .wp-block-custom-heading-with-line {
    text-align: center;
    position: relative;
}

.edit-post-visual-editor .wp-block-custom-heading-with-line h1,
.edit-post-visual-editor .wp-block-custom-heading-with-line h2,
.edit-post-visual-editor .wp-block-custom-heading-with-line h3,
.edit-post-visual-editor .wp-block-custom-heading-with-line h4,
.edit-post-visual-editor .wp-block-custom-heading-with-line h5,
.edit-post-visual-editor .wp-block-custom-heading-with-line h6 {
    background: white;
    display: inline-block;
    max-width: 780px;
    padding: 0 50px;
    margin: 0;
}

.edit-post-visual-editor .wp-block-custom-heading-with-line::after {
    content: '';
    position: absolute;
    background: black;
    height: 1px;
    left: 0;
    right: 0;
    top: 50%;
    z-index: -1;
}