Styling a form in Bootstrap is also very easy, we just have to add the .form-group class to the container <form> or <div> and the .form-control class to each input-type element:

<h2>{{title}}</h2>
<div class="question-edit">
    <div class="form-group">
        <label for="text">Question text:</label>
        <br />
        <textarea id="text" 
                  [(ngModel)]="question.Text" 
                  placeholder="enter a suitable text..."
                  class="form-control"
                  ></textarea>
    </div>

[...]

Jumping to the LESS style sheet file, it won't hurt to increase the height of the text areas-- to increase their overall usability--and also put a limit to the horizontal spanning of some specific elements, such as the right panel (for high-res viewports) and the <select>:

.answer-edit {
    width: 80%;

    @media (max-width: 767px) {
        width: 100%;
    }

    textarea {
        min-height: 100px;
    }

    select {
        max-width: 200px;
    }

    .commands {
        margin-top: 20px;
    }
}

That's about it.