Salesforce Visualforce checkbox not clickable

enter code here( <div class="slds-form-element">
                    <div class="slds-form-element__control">
                        <span class="slds-checkbox">

{!$Label.SendEmailNotificationToCaseCreator} enter image description here )

In this code if i remove only then the checkbox is clickable and that too without any styles. How to make it work normally? I added the screenshot of checkbox without having span class and which is working not according to the styles. I have other checkbox on the same vf page which have the exactly same code but they work properly.