MUI Button has 3 variants.

Contained

Button with background color. Used for important actions.

<Button variant="contained">重要!!</Button>

Outlined

Outlined Button. Used for medium importance action.

<Button variant="outlined">中程度の重要度</Button>

Text

Button with no background or border. Used for low importance action.

<Button variant="text">重要度が低い</Button>