Newbie Project, Facebook ad using HTML and CSS; Need Help

Hello! I am a beginner (just finished my free trial) and in order to recap what I learned in the HTML and CSS course, I decided to create a Facebook ad. I think my project has gone ok, I have all the contents I want on the page, but I really hate is that I want to cover up the body with all of the content, I want the content to take up the full space of the browser or at least be in the center but I have no idea how to do this. Below is my code so far:
One thought was to try and set div class=container to width: 100%; and height: 100%; since it contains all of the content, but this doesn’t seem to work.

<!DOCTYPE html>
<html>
   <head>
      <style>
        body {
          background-color: black;
  
        }
        div.image {
          position: absolute;
        }
        div.content {
          position: absolute;
          top: 185px;
          left: 140px;
          border: gray 5px none;
          background-color: hsla(240, 0%, 0%, .70);
          box-sizing: border-box;
          padding: 30px;
        }
        div.contact-info {
          z-index: 20;
          position: absolute;
          top: 540px;
          left: 525px;
        }
      </style>
   </head>
   <body>
     <div class="container">
     <div class="image">
       <img src="https://files.constantcontact.com/c843c2a4701/94e8832e-d94d-496c-8c1d-36b28903a447.jpg" alt="drug-alcohol-treatment"></img>
     </div>
     <div class="content">
       <p style="text-align: center; line-height: 1.2; word-break: break-word; font-size: 20px; mso-line-height-alt: 24px; margin: 0;">
         <span style="font-size: 50px;"><strong><span style="color: #ffffff;">
         <span style="">Back Together!</span></span></strong></span></p>

         <p style="text-align: center; line-height: 1.2; word-break: break-word; font-size: 20px; mso-line-height-alt: 24px; margin: 0;">
           <span style="font-size: 50px;"><strong><span style="color: #ffffff;">
           <span style="">Reopening In Person for All Services</span></span></strong></span></p>

           <p style="text-align: center; line-height: 1.2; word-break: break-word; font-size: 20px; mso-line-height-alt: 24px; margin: 0;">
             <span style="font-size: 50px;"><strong><span style="color: #ffffff;">
             <span style="">Monday, June 8th</span></span></strong></span></p>

             <p style="text-align: center; line-height: 1.2; word-break: break-word; font-size: 20px; mso-line-height-alt: 24px; margin: 0;">
               <span style="font-size: 50px;"><strong><span style="color: #ffffff;">
               <span style="">Now Offering Telehealth & Virtual Services</span></span></strong></span></p>
     </div>
     <div class="contact-info">
       <p style="text-align: center; line-height: 1.2; word-break: break-word; font-size: 20px; mso-line-height-alt: 24px; margin: 0;">
         <span style="font-size: 25px;"><strong><span style="color: #000;">
         <span style=""><a href="https://www.woodlandsrecoverycenters.com/" target="_blank">Visit Us Today!</a></span></span></strong></span></p>
     </div>
   </div>
  </body>
</html>