JSFiddle - React, Tailwind, and code Playground

HTML

<div id="first" >Поисковая форма</div>
<div id="triangle" >Расширенный поиск</div>

CSS

#first{
  width:500px;
  height:100px;
  background-color: #333;
}
#triangle {
	width: 200px;
	height: 50px;
 	border-top: 20px solid #333; 
	border-right: 20px solid transparent;		
}