JSFiddle - React, Tailwind, and code Playground

HTML

<div id="form_wrapper">
    <form accept-charset="UTF-8" action="/some_action" method="post">
        <div class="category_dropdown_container">
            <select class="chosen chzn-done" name="question[category_id]" id="selQJK">
                <option value="0">Blah blah blah blah</option>
                <option value="1">General</option>
                <option value="2">Fruits</option>
                <option value="3">Ice Creams</option>
                <option value="4">Candy</option>
            </select>
        </div>
        <div class="resizable_text_box">
            <input id="question_text_box" name="question[what]" placeholder="Write a query..." type="text" />
        </div>
        <input name="commit" type="submit" value="Ask!" />
    </form>
</div>

CSS

#form_wrapper {
    border: 1px solid blue;
    width: 600px;
    padding: 5px;
}
form {
    display: inline-block;
    width: 100%;
}
.category_dropdown_container {
    float:left;
}
.resizable_text_box {
    overflow:hidden;
    border: 1px solid red;
}
.resizable_text_box > input[type="text"] {
    width:100%;
}
input[type="submit"] {
    background-color: lightblue;
    width: 80px;
    float: right;
}