Hello, 
I have created a visualforce page custom button on List View of Lead object. This button is visible in Salesforce Classic and Liightning both. When I click on the button in Lightning, it is working as expected and redirecting to the url specified in it's visualforce page. But when I click on this button in Classic it is not working as expected and returns on the List View page itself. Previously when I created it, it was working well and so did not create a javascript button specifically for classic, instead made a visualforce page which can be good for both, but now the visualforce page is not working. What can be the issue and how to resolve it ? Is there any impact of Winter'20 release ? 

I was reading https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/tokens_intro.htm (https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/tokens_intro.htm" target="_blank) . But, I found this similar to using static resources, like the same type of styling can also be done using staic resources and the CSS also looks the same like in Salesforce Classic, so what is the difference ? Why should I use Design Tokens ? What are the advantages of Design Tokens ? Can someone please help me over this ? 
 

I was reading https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/tokens_intro.htm (https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/tokens_intro.htm" target="_blank) . But, I found this similar to using static resources, like the same type of styling can also be done using staic resources and the CSS also looks the same like in Salesforce Classic, so what is the difference ? Why should I use Design Tokens ? What are the advantages of Design Tokens ? Can someone please help me over this ? 
 

I'm using MS Windows 8.1 with Google Chrome Version 35.0.1916.114 m
I have a free Salesforce trial version

From the "My Name" menu I chose "Developer Console".
I get a new window Force.com Developer Console with the "Loading workspace ..." progress bar.
The progress bar gets hung at about 50%.

Any advice?

Oded