accessibility: read message box header title correctly (#21)

src/assets/css/bootstrap-theme-slate.css

@@ -5801,6 +5801,8 @@ button.close {
 .modal-title {
   margin-bottom: 0;
   line-height: 1.5;
+  font-size: 1.17rem;
+  font-weight: 500;
 }
 
 .modal-body {

src/react/components/common/messageBox/messageBox.tsx

@@ -68,7 +68,7 @@ export default class MessageBox extends React.Component<IMessageBoxProps, IMessa
             <Modal className="messagebox-modal"
                 isOpen={this.state.isOpen}
                 onClosed={this.onClosed}>
-                <ModalHeader toggle={this.toggle}>{this.props.title}</ModalHeader>
+                <ModalHeader tag="div" toggle={this.toggle}>{this.props.title}</ModalHeader>
                 <ModalBody>{this.getMessage(this.props.message)}</ModalBody>
                 {!this.props.hideFooter && <ModalFooter onClick={this.onFooterClick}>
                     {this.props.children}