Design fixes (#555)

* Change placeholder color and design fixes for show page / sidebar

* Replace hardcoded border radiuses

* Improve border display for middle of button group

* Editor styling

* Editor font size

* Comment Bar positioning and remove scrollbar for 1px

* Add Comments section title

* Nit: match css style

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Co-authored-by: Emilien <emilien.chauvet.enpc@gmail.com>

front/src/modules/people/components/PersonChip.tsx

@@ -26,7 +26,7 @@ const baseStyle = ({ theme }: { theme: Theme }) => `
     filter: brightness(95%);
   }
   img {
-    border-radius: 100%;
+    border-radius: ${theme.border.radius.rounded};
     height: 14px;
     object-fit: cover;
     width: 14px;