Revert hr elements on homepage to original light grey
Revert hr elements on homepage to original light grey

ibm-watson-data-lab/ibm-watson-data-lab.github.io,ibm-watson-data-lab/ibm-watson-data-lab.github.io,ibm-watson-data-lab/ibm-watson-data-lab.github.io,ibm-watson-data-lab/ibm-watson-data-lab.github.io