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/inputs/TextInput.tsx

@@ -26,7 +26,7 @@ const StyledLabel = styled.span`
 const StyledInput = styled.input<{ fullWidth: boolean }>`
   background-color: ${({ theme }) => theme.background.tertiary};
   border: none;
-  border-radius: 4px;
+  border-radius: ${({ theme }) => theme.border.radius.sm};
 
   color: ${({ theme }) => theme.font.color.primary};
   font-family: ${({ theme }) => theme.font.family};