preview-collapse.css

/* Make collapsed section more apparent */
.markdown-preview-view ul .is-collapsed::after {
    background-color: var(--background-secondary);
    border-radius: 0.25rem;
    padding: 0px 6px 3px 5px;
    margin-left: 0.5rem;
}
.markdown-preview-view .collapse-indicator {
    margin-top: -0.2rem;
}