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/inplace-inputs/components/InplaceInputDateEditMode.tsx

@@ -17,7 +17,7 @@ export type StyledCalendarContainerProps = {
 const StyledCalendarContainer = styled.div<StyledCalendarContainerProps>`
   background: ${({ theme }) => theme.background.secondary};
   border: 1px solid ${({ theme }) => theme.border.color.light};
-  border-radius: 8px;
+  border-radius: ${({ theme }) => theme.border.radius.md};
   box-shadow: ${({ theme }) => theme.boxShadow.strong};
   left: -10px;
   position: absolute;