[Alert] Fix support for nested elements

docs/src/pages/components/alert/DescriptionAlerts.js

@@ -18,19 +18,19 @@ export default function DescriptionAlerts() {
     <div className={classes.root}>
       <Alert severity="error">
         <AlertTitle>Error</AlertTitle>
-        This is an error alert — check it out!
+        This is an error alert — <strong>check it out!</strong>
       </Alert>
       <Alert severity="warning">
         <AlertTitle>Warning</AlertTitle>
-        This is a warning alert — check it out!
+        This is a warning alert — <strong>check it out!</strong>
       </Alert>
       <Alert severity="info">
         <AlertTitle>Info</AlertTitle>
-        This is an info alert — check it out!
+        This is an info alert — <strong>check it out!</strong>
       </Alert>
       <Alert severity="success">
         <AlertTitle>Success</AlertTitle>
-        This is a success alert — check it out!
+        This is a success alert — <strong>check it out!</strong>
       </Alert>
     </div>
   );

docs/src/pages/components/alert/DescriptionAlerts.tsx

@@ -20,19 +20,19 @@ export default function DescriptionAlerts() {
     <div className={classes.root}>
       <Alert severity="error">
         <AlertTitle>Error</AlertTitle>
-        This is an error alert — check it out!
+        This is an error alert — <strong>check it out!</strong>
       </Alert>
       <Alert severity="warning">
         <AlertTitle>Warning</AlertTitle>
-        This is a warning alert — check it out!
+        This is a warning alert — <strong>check it out!</strong>
       </Alert>
       <Alert severity="info">
         <AlertTitle>Info</AlertTitle>
-        This is an info alert — check it out!
+        This is an info alert — <strong>check it out!</strong>
       </Alert>
       <Alert severity="success">
         <AlertTitle>Success</AlertTitle>
-        This is a success alert — check it out!
+        This is a success alert — <strong>check it out!</strong>
       </Alert>
     </div>
   );

packages/material-ui-lab/src/Alert/Alert.js

@@ -123,9 +123,6 @@ export const styles = (theme) => {
     /* Styles applied to the message wrapper element. */
     message: {
       padding: '8px 0',
-      display: 'flex',
-      flexDirection: 'column',
-      justifyContent: 'center',
     },
     /* Styles applied to the action wrapper element if `action` is provided. */
     action: {