The ODS HTML statement opens the HTML destination and creates HTML output. The output from PROC PRINT goes to the body file. FRAME= and CONTENTS= create a frame that includes a table of contents that links to the contents of the body file. The body file also appears in the frame.

The STYLE= option tells ODS to use customdefault as the style definition when it formats the output. 

ods html body='customdefaultstyle-body.htm'
         contents='customdefaultstyle-content.htm'
         frame='customdefaultstyle-frame.htm'
         style=customdefault;