When I am trying to use Salesforce Lightning Design System in my vf page, I get error –
Unknown component apex:sldswhile including
<apex:slds />on my vf page.
Unrelated – I have also tried uploading the slds css as static resource and including it in page, it messes up the standard header. Please see screenshot below
Note that this component is only available starting with API Version 39.0. If you try to include it in API Version 38.0 and below, it will not be available.