[FIX] composer: overflow on composer at end of screen

The button to close the composer's formula assistant would overflow
from the viewport and make an additional scrollbar appear when it's
at the end of the screen (eg. standalone composer in the CF color
scale panel).

This was due to two things:
1) there was a comment with `//`, which is invalid css and disabled
the `width` property of the button
2) we were using a `CLOSE_ICON_RADIUS` to compute the position of the
formula assistant. But this constant wasn't actually used in the CSS,
so the button could have an arbitrary width unrelated to the constant.
(in practice it was 18.4px vs 18px, but this would change if we changed
the font size).

closes #5252

Task: 4315958
Signed-off-by: Rémi Rahir (rar) <[email protected]>

Author: hokolomopo

src/components/composer/composer/composer.ts

@@ -92,10 +92,10 @@ css/* scss */ `
     }
 
     .fa-stack {
-      // reset stack size which is doubled by default
-      width: 1em;
-      height: 1em;
-      line-height: 1em;
+      /* reset stack size which is doubled by default */
+      width: ${CLOSE_ICON_RADIUS * 2}px;
+      height: ${CLOSE_ICON_RADIUS * 2}px;
+      line-height: ${CLOSE_ICON_RADIUS * 2}px;
     }
 
     .force-open-assistant {