如何在sencha touch中修改placeHolder的颜色

index.js

Ext.setup({
onReady: function() {
new Ext.form.FormPanel({
fullscreen: true,
items: [{
xtype: 'textfield',
label: 'Name',
cls: 'customField',
placeHolder: 'Insert your name here'
},{
xtype: 'textfield',
label: 'Surname',
placeHolder: 'Insert your surname here'
}]
});
}
});

style.css

.customField input::-webkit-input-placeholder {
color: #2e4bc5;
}