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/table/EntityTable.tsx

@@ -35,7 +35,7 @@ type OwnProps<TData extends { id: string }, SortField> = {
 const StyledTable = styled.table`
   border-collapse: collapse;
 
-  border-radius: 4px;
+  border-radius: ${({ theme }) => theme.border.radius.sm};
   border-spacing: 0;
   margin-left: ${({ theme }) => theme.table.horizontalCellMargin};
   margin-right: ${({ theme }) => theme.table.horizontalCellMargin};