JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" name="prefix" id="prefix" value="8-910" disabled><input type="text" name="phone" id="phone" maxlength="7" value="">

CSS

input#prefix, input#phone {
    margin:0;
}
input#prefix {
    width:35px;
}
input#phone {
    width:140px;
}