Bring MinervaNeue & MobileFrontend error/warning/success messages/message box visual appearance close to Style Guide components template.
Originated in T127405 with current treatment is off template and has too low contrast accessibility issues
{F4669690 width=50%}
== Proposed unified colors
Applying [[ https://design.wikimedia.org/style-guide/components/messages.html | Style Guide definitions of message boxes ]]:
{F29760612}
== Steps to accomplish
[] Both, MinervaNeue & MobileFrontend are currently importing mediawiki.ui variables and define their own. Let's remove special overrides and just references mediawiki.ui vars until MN/MF gets independent from it. Defining in 3 places makes 0 sense
[] Align only colors and borders for now, padding seems contextual. Can revisit in a box unification at a later point