【网摘】模仿 placeholder 属性

/*为空时显示 element attribute content*/

.project-task-edit .subtask-body-txt:empty:before {
	content: attr(placeholder);
	color: #eee;
}

.project-task-edit .subtask-body-txt:not:empty:before {
	content: '';
	color: #eee;
}

/*焦点时内容为空*/

.subtask-body-txt:focus:before {
	content: none;
}