Salesforce Fact #688 | Pagemessage strength

Apex:pageMessage has an attribute 'Strength'. This controls the visibility and size of the icon displayed next to message. The value can vary from 0 to 3, 3 being the highest. If we don't need to show the icon, we can use the value 0.

Reference: https://developer.salesforce.com/docs/atlas.en-us.pages.meta/pages/pages_compref_pageMessage.htm

Attached is the screenshot.