Add Sticky Effect for the First Three Columns on Leaderboard

[HuanzhiMao]

This PR adds a sticky effect for the first three columns (rank, overall accuracy and model name) on the leaderboard. This feature is handy when viewing the leaderboard on small screen devices as it helps the user to know which model they are looking at when scrolling to the far right. This PR DOES NOT change the leaderboard score/ranking; this is just a styling update.