Although I am not Joschua I use his CSS and have customized it for me
/* Preview Mode */
.markdown-preview-view h6
{
position: relative;
left: -3.1%;
top: 40px;
line-height: 0px;
margin-top: -20px;
margin-right: 3px;
font-family: var(--font-family-preview);
font-weight: 500;
font-size: 13px;
font-weight: bold;
color: var(--text-faint) !important;
}
/* Editor */
.cm-s-obsidian .cm-header-6
{
position: absolute; /* was relative */
left: -21px;
line-height: 0px;
margin-top: 40px !important;
margin-right: 3px;
font-family: var(--font-family-preview);
font-weight: 500;
font-size: 10px;
font-weight: bold;
color: var(--text-faint) !important;
}