JSFiddle - React, Tailwind, and code Playground
HTML
<form id="form">
<input type="text" placeholder="text" />
<input type="submit" value="Click here" />
</form>
CSS
#form {
width: 60%;
display: flex;
flex-direction: row;
border: 1px solid grey;
padding: 2px;
/*border-radius: 50px;*/
}
input {
flex-grow: 2;
border: none;
border-radius: 50px;
}