I would like to add a custom css with v4.master however do not want to edit the actual master page itself.
the idea is to load the custom css on the wiki page.
do we have any way of doing it?
In addition to Eric's post
You can use also use
ScriptLink together with Custom action and inject your CSS into the
ScriptLink section of masterpage - All without editing a master page (see the sample below)
<CustomAction Id="MyCustomCSSWiki" Location="ScriptLink" ScriptBlock="document.write('<link rel="stylesheet" After="Corev15.css" type="text/css" href="../_layouts/14/MyCustom/Styles/BrandingWiki.css"></' + 'link>');" Sequence="202" />
If you don't want to modify the master page, then the alternative is to go into Site Settings and click on Master Page in the look and feel section and in there add your custom css file into the Alternate CSS URL section.
If you just want to add custom CSS to a specific page, then add a Content Editor web part and point that to your CSS file.