.navbar {
    overflow: hidden;
    background-color: darkorange;
    position: fixed; /* Set the navbar to fixed position */
    top: 0; /* Position the navbar at the top of the page */
    width: 100%; /* Full width */
}

/* Links inside the navbar */
.navbar a {
    float: right;
    display: block;
    color: dodgerblue;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    font-style: oblique;
}

/* Change background on mouse-over */
.navbar a:hover {
    background: #ddd;
    color: dodgerblue;
}
/* Main content */
.main {
    margin-top: 30px; /* Add a top margin to avoid content overlay */
}
<div class="container">
  <form action="action_page.php">

    <label for="fname">First Name</label>
    <input type="text" id="fname" name="firstname" placeholder="Your name..">

    <label for="lname">Last Name</label>
    <input type="text" id="lname" name="lastname" placeholder="Your last name..">

    <label for="country">Country</label>
    <select id="country" name="country">
      <option value="australia">Australia</option>
      <option value="canada">Canada</option>
      <option value="usa">USA</option>
    </select>

    <label for="subject">Subject</label>
    <textarea id="subject" name="subject" placeholder="Write something.." style="height:200px"></textarea>

    <input type="submit" value="Submit">

  </form>
</div>

Step 2) Add CSS:
Example
/* Style inputs with type="text", select elements and textareas */
input[type=text], select, textarea {
    width: 50; /* Full width */
    padding: 12px; /* Some padding */  
    border: 1px solid #ccc; /* Gray border */
    border-radius: 4px; /* Rounded borders */
    box-sizing: border-box; /* Make sure that padding and width stays in place */
    margin-top: 6px; /* Add a top margin */
    margin-bottom: 16px; /* Bottom margin */
    resize: vertical /* Allow the user to vertically resize the textarea (not horizontally) */
}

/* Style the submit button with a specific background color etc */
input[type=submit] {
    background-color: #4CAF50;
    color: white;
    padding: 12px 20px;
    border: none;
    border-radius: 4px;
    cursor: pointer;
}

/* When moving the mouse over the submit button, add a darker green color */
input[type=submit]:hover {
    background-color: #45a049;
}

/* Add a background color and some padding around the form */
.container {
    border-radius: 5px;
    background-color: #f2f2f2;
    padding: 20px;
}