marginが消えない・勝手に生成される

div class="container"のmarginを消したいのですが、消えないどころかmargin:0;を指定しても1枚目の画像のように勝手にmarginが生成されてしまいます。1枚目ですと右側に勝手にmarginが作られているので、ならばとmargin-right:0;を追記すると、なぜか2枚目の画像のように今度は反対側にmarginが生成されます。ちなみにmarginを指定しないと両側にmarginが生成されmargin:0 autoのように中央に配置されます。
containerのmarginを消して（勝手に生成しないようにして）画面いっぱいにしたいのですが、どうすればよいでしょうか。

chat.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>

<%@ page import="java.util.*" %>
<%@ page import="model.*" %>
<%@ page import="java.sql.Timestamp" %>
<%@ page import="java.io.InputStream" %>
<%@ page import="java.io.InputStreamReader" %>
<%@ page import="java.io.BufferedReader" %>

<!DOCTYPE html>
<%
	List<MessageDto> dtoList = (List<MessageDto>)request.getAttribute("ShowAllMessage");
	HttpSession sess           = request.getSession();
	UserInfoDto userInfoOnSession = (UserInfoDto)sess.getAttribute("LOGIN_INFO");
%>

<html>
<head>
	<meta charset="UTF-8">
	<meta name=”viewport” content="width=device-width,initial-scale=1.0,minimum-scale=1.0">
	<title>chatroom</title>
	<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
	<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" integrity="sha384-WskhaSGFgHYWDcbwN70/dfYBj47jz9qbsMId/iRN3ewGhXQFZCSftd1LZCfmhktB" crossorigin="anonymous">
	<link rel="stylesheet" href="<%=request.getContextPath() %>/css/room.css">

</head>
<body>
<nav class="navbar navbar-expand-lg navbar-light bg-light">
～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～
 </nav>


	<div class="container">　//←これのmarginをどうにかしたい

		<div class="chat_screen">
			<%
			//javaの処理のため割愛
			%>

			<div class="chat_box">
				<div class="username_box">
					<p class="username"> <%=userName%></p>
				</div>
				<%if(image != null){ %>
					<img src="data:image/*;base64,<%=image%> ">
				<%} %>
				<div class="message_box">
					<p class="message" id="message_text"> <%=message%></p>
				</div>
				<div class="created_at_box">
					<p class="created_at"> <%=time%></p>
				</div>
				<%if(userName.equals(userInfoOnSession.getUserName())) {%>
					<form action="EditMessage" method="post">
						<div class="edit_message_box">
							<input type="hidden" name="message_id" value="<%=messageId %>">
							<input type="hidden" name="edit_message_text" id="edit_message_text" value="" >
							<input type="submit" class="edit_message_button btn btn-outline-secondary" value="メッセージを編集する" onclick="return editConfirm();">
						</div>
					</form>
				<%} %>
				<%if(userName.equals(userInfoOnSession.getUserName())) {%>
					<form action="DeleteMessage" method="post">
						<div class="delete_message_box">
							<input type="hidden" name="message_id" value="<%=messageId %>">
							<input type="submit" class="delete_message_button btn btn-outline-secondary" value="メッセージを削除する" onclick="return confirmCheck();">
						</div>
					</form>
				<%} %>
			</div>
		<% } %>
	</div>
	<div class="submit_box">
			<form action="InputMessage" enctype="multipart/form-data" method="post">
					<div class="textarea_box">
						<textarea id="input_message_text" name="message" size="40" maxlength="500" class="input_message_text form-control"></textarea>
					</div>
					<div class="submit_image_box">
						<input type="file" name="image" accept="image/*" class="image_submit_button" id="image_submit">
					</div>
					<div class="submit_button_box">
						<input type="submit" id="message_submit"value="投稿する" class="send_message_button btn btn-info" onclick="return brankCheck();">
					</div>
			</form>
			<form action="DeleteMessage" method="get">
				<div class="delete_button_box">
						<input type="submit" id="delete_button"value="全件削除" class="send_delete_button">
				</div>
			</form>
		</div>
</div>

<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js" integrity="sha384-ZMP7rVo3mIykV+2+9J3UJ46jBk0WLaUAdn689aCwoqbBJiSnjAK/l8WvCWPIPm49" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js" integrity="sha384-smHYKdLADwkXOn1EmN1qk/HfnUcbVRZyYmZ4qpPea6sjB/pTJ0euyQp0Mk8ck+5T" crossorigin="anonymous"></script>
<script type="text/javascript" src="<%=request.getContextPath()%>/js/Messagebrank.js" ></script>
<script type="text/javascript" src="<%=request.getContextPath()%>/js/deleteConfirm.js" ></script>
<script type="text/javascript" src="<%=request.getContextPath()%>/js/editConfirm.js" ></script>
<script type="text/javascript" src="<%=request.getContextPath() %>/js/xssEscape.js" > </script>
</body>
</html>

room.css
1*{
2	margin:0;
3	padding:0;
4}
5body{
6	background:#9ee0d6;
7	font-family:"Meiryo";
8	width:100%;
9
10
11}
12head{
13
14}
15.chatroom_title_box{
16
17
18}
19.navbar-brand{
20	font-size:40px;
21}
22.collapse{
23
24}
25.navber-brand{
26	display:inline-block;
27}
28.container{
29	width:100%;
30	min-height:100vh;
31	margin:0;  
32	padding:0;
33	display:flex;
34	overflow:hidden;
35}
36.chat_screen{
37	min-height:100vh;
38	background:white;
39	width:100%;
40	float:right;
41	margin-right:0;
42
43}
44.chat_box{
45
46}
47.username_box{
48
49}
50.username{
51
52}
53.image{
54
55}
56.message_box{
57
58}
59.message{
60
61}
62.created_at_box{
63
64}
65.create_at{
66
67}
68.submit_box{
69	margin:40px 30px 30px 30px;
70}
71.textarea_box{
72	width:100%;
73
74}
75