Trying to blend your web page font with your adsense font type and size? Below is the summary from Quick Online Tips. Apply it to your CSS file. 

For the leaderboard
Title: style="line-height:12px; font-size:11px; font-family:verdana,arial,sans-serif"
Description: style="line-height:12px; font-size:10px; font-family:verdana,arial,sans-serif"
URL: style="line-height:12px; font-size:10px" face="verdana,arial,sans-serif"

For the large rectangle
Title: style="line-height:14px;font-size:11px" face="arial,sans-serif"
Description: style="line-height:14px;font-size:11px" face="arial,sans-serif"
URL: style="line-height:14px;font-size:10px" face="arial,sans-serif"