[Solved] Formatting of HTML page is lost in outlook email

I am trying to send an HTML email though C# code. Everything works fine. I can send the email with a logo and icons. The only issue, I am facing is that formatting of the Header is lost when I send the email to Outlook. Below is my code:

This is how the screen looks like on HTML page:

when I send the email to Outlook then the screen looks like this:

Both the company name and city name moves underneath the icon. I tried changing the flex Direction to Row, but that did not fix anything. I also tried outlook zoom setting and it is set to 100%. This is the C# code to send the email:

Any help why the formatting of the header is lost in HTML will be highly appreciated.

HTML

<div class="container">
    <div class="logo">
        <img src="Images/delete.png" alt="RAC" width="80" height="80" />
    </div>
    <div class="names">      
        <div class="name1">This is City Name</div>
        <div class="name2">This is company Name</div>
    </div>
</div>

I am developing this in ASP.net web forms. 

This is the style sheet:

CSS

.container { display: flex; align-items: center; padding: 10px; background-color: #335970; width: 100%; }

.logo { margin-right: 10px; }

.names { display: flex; flex-direction: column; }

.name1 { font-size: 25px; color: #e9c46a; }

.name2 { font-size: 25px; color: white; }

Code

C#

SmtpClient client = new SmtpClient();

client.Credentials = new NetworkCredential("test", EmailPass);
client.Port = 200;
client.EnableSsl = true;
client.Host = "smtp.office365.com";
client.DeliveryMethod = SmtpDeliveryMethod.Network;

MailMessage mail = new MailMessage();

mail.IsBodyHtml = true;
mail.From = test;

mail.To.Add(new MailAddress("t@t.com"));
mail.Subject = "test";
using (StreamReader reader = new StreamReader(Server.MapPath("~/EmailTemplate.html")))
{
    body = reader.ReadToEnd();
}

mail.Body = body;

client.Send(mail);