I don’t use Live view on obsidian. I prefer “Legacy Mode”. I used to use a custom css file to change fonts on both source-view & preview-view.
It use to work well before 2022. Now it does not work.
My Custom CSS 
.markdown-source-view {
font-family: 'MonoLisa', monospace !important;
}
.markdown-preview-view {
font-family: 'Rubik', sans-serif !important;
}
.markdown-source-view .cm-header-1,.cm-header-2,.cm-header-3 {
font-family: 'Sunflora', sans-serif !important;
}
.markdown-preview-view h1 {
font-family: 'Sunflora', sans-serif !important;
}
Here, only the first part does not work that is
.markdown-source-view {
font-family: 'MonoLisa', monospace !important;
}
Font change in preview-view & strangely the “h1” code in source-view works.
How can I change font on source-view via Custom CSS ?