Hi @renfield, this still works for me in Edit Mode as well as Preview Mode. Maybe your theme or a plugin is styling the headers as well now.
.cm-s-obsidian pre.HyperMD-header-1, .markdown-preview-view h1 {
padding-top: 80px !important;
}
Odd as it might seem, someone recently had a case where removing the !important solved the issue.
TRY:
.cm-s-obsidian pre.HyperMD-header-1, .markdown-preview-view h1 {
padding-top: 80px;
}