Update _config.yml

Author: hh4ts

_config.yml

@@ -3,5 +3,5 @@ description: "2025 KDD Lecture-style Tutorial | Toronto, Canada <br/>
 Kun Yi, Qi Zhang, Wei Fan, Longbing Cao, Shoujin Wang, Hui He, Guodong Long, Liang Hu, Qingsong Wen, Hui Xiong <br/>
 Sunday, August 3, 2025 | 8:00 AM - 11:00 AM <br/>"
 header_text: KDD 2025 Tutorial
-theme: jekyll-theme-cayman
+theme: jekyll-theme-slate
 google_analytics: G-Y00QMX21NQ