how to override existing css for validator callout extender css class for custom validation.

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ASP.NET

CSS

Use Custom validation for show error message & applied valid callout extender for that custom validator validation working fine but callout popup display on top left corner i also fine out solution on that set the ajax__validatorcallout_popup_table {visibility: visible; position: absolute; right: -38px; z-index: 1000; top: 100px;}
run time when apply custom css for that custom validator then existing css is not override.