<form>
    <fieldset>
        <legend>관심이 있는 웹 개발 언어를 선택하세요.</legend>
        <div>
           <input type="radio" id="html" name="interest" value="html">
           <label for="html">HTML</label>
        </div>
        <div>
           <input type="radio" id="css" name="interest" value="interest">
           <label for="css">CSS</label>
        </div>
        <div>
           <input type="radio" id="js" name="interest" value="interest">
           <label for="js">JavaScript</label>
        </div>
        <button type="submit">제출</button>
    </fieldset>
</form>
브라우저에서 실제 표시된 모습
<form>
    <fieldset disabled>
        <legend>필수 정보</legend>
        <div>
            <label for="user-name">이름</label>
            <input type="text" id="user-name" value="홍길동">
        </div>
        <div>
            <label for="user-pw">비밀번호</label>
            <input type="password" id="user-pw" value="test">
        </div>
    </fieldset>
</form>
브라우저에서 실제 표시된 모습
fieldset {
    padding: 1em;
    background-color: #f1f9eb;
    border: 1px solid yellowgreen;
    border-radius: 10px;
    min-width: 0;
}
fieldset + fieldset {
    margin-top: 1em;
}
legend {
    background-color: yellowgreen;
    padding: 0.2em 1em;
    border-radius: 5px;
}
input {
    display: block;
    width: 100%;
}
<form>
    <fieldset>
        <legend>Legend One</legend>
        <label for="input-one">Input One</label>
        <input type="text" id="input-one">
    </fieldset>
    <fieldset>
        <legend>Legend Two</legend>
        <label for="input-two">Input Two</label>
        <input type="text" id="input-two">
    </fieldset>
    <fieldset>
        <legend>Legend Three</legend>
        <label for="input-three">Input Three</label>
        <input type="text" id="input-three">
    </fieldset>
</form>
브라우저에서 실제 표시된 모습