Warning about mentioning many people in a comment looks bad

The warning displayed when many people are mentioned in a comment needs styling.

Dev: https://dev.gitlab.org/gitlab/gitlabhq/issues/2593

Proposed Steps

• Correctly align with the write && preview headers of comment textbox
• Add a nice text color for easier visibility

@DouweM @skyruler

Update from discussion on dev

• You'll see the warning when you type this example @all test and then blur (unfocus) the textarea.

The main problems I have are the vertical alignment and the text color.

Correctly align with the write && preview headers of comment textbox

Milestone changed to Interaction

Milestone removed

Milestone changed to Interaction

mentioned in merge request !1654 (merged)

Added ~121287 label

Milestone changed to 8.3

Added ~19492 and removed ~121287 labels

Reassigned to @creamzy

I would prefer to move it above the action btns, and below the input field. In this case

1. we put it more prominently without usage of extra color
2. we get rid of responsive layout problem, when message cuts the field from the tabs
3. this positioning is much better in terms of a user eye movement along the page.

will continue after setting up environment

Added frontend and removed ~19492 labels

Assignee removed

Reassigned to @dbalexandre

mentioned in merge request !1971 (merged)

Status changed to closed by merge request !1971 (merged)

mentioned in commit 4c353143