To render items in three columns, I attempted to add the following CSS3 directives to my project\'s README.md file, but the styling was stripped out:
GitHub-Flavored Markdown only permits certain whitelisted tags and attributes in inline HTML:
HTML
You can use a subset of HTML within your READMEs, issues, and pull requests.
A full list of our supported tags and attributes can be found in the README for github/markup.
Regarding <div> tags, that README says that only the itemscope and itemtype attributes are whitelisted, in addition to the general attribute whitelist:
abbr,accept,accept-charset,accesskey,action,align,alt,axis,border,cellpadding,cellspacing,char,charoff,charset,checked,cite,clear,cols,colspan,color,compact,coords,datetime,dir,disabled,enctype,for,frame,headers,height,hreflang,hspace,ismap,label,lang,longdesc,maxlength,media,method,multiple,name,nohref,noshade,nowrap,prompt,readonly,rel,rev,rows,rowspan,rules,scope,selected,shape,size,span,start,summary,tabindex,target,title,type,usemap,valign,value,vspace,width,itemprop
No tags support the style attribute.
Unless you can hack something together with the tags and attributes listed in that README I think you'll find that you're out of luck.
An alternative would be to put together a GitHub Pages site, which seems to be much more flexible.