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/ui/components/editor/BlockEditor.tsx

@@ -9,11 +9,11 @@ interface BlockEditorProps {
 const StyledEditor = styled.div`
   min-height: 200px;
   width: 100%;
-  & .editor-create-mode,
-  .editor-edit-mode {
+  & .editor {
     background: ${({ theme }) => theme.background.primary};
+    font-size: 13px;
   }
-  & .editor-create-mode [class^='_inlineContent']:before {
+  & .editor [class^='_inlineContent']:before {
     color: ${({ theme }) => theme.font.color.tertiary};
     font-style: normal !important;
   }