substance/packages/prose-editor/_prose-editor.css

Substance is a JavaScript library for web-based content editing. It provides building blocks for realizing custom text editors and web-based publishing systems.

.sc-prose-editor {}
.sc-prose-editor .sc-container-editor {
  padding:  var(--default-padding);
  margin: 0 auto;
  max-width: 800px;
}

/* Add padding to each child except last one */
.sc-prose-editor .sc-container-editor > * {
  margin: 10px 0;
}
.sc-prose-editor .se-toolbar-wrapper {
  border-bottom: 1px solid  var(--border-color);
  background: #fafbfc;
  z-index: 200;
}

.sc-prose-editor .se-toolbar-wrapper .sc-toolbar {
  max-width: 800px;
  margin: 0 auto;
}