JSFiddle - React, Tailwind, and code Playground

HTML

<label>
    <input />    
</label>

CSS

label:before{
    content: "+387";
}
label {
    border: 1px solid rgba(0,0,0,0.4);
    box-shadow: 1px 1px 1px rgba(0,0,0,0.207);
}
input{
    background: transparent;
    outline: none;
    border: none;
}