Html wrap div full width - html

Question

I have an HTML page with a div containing another div that contains all users in a database (chat system) however the ul li tag is not taking the full width of the parent div. This is an image of the expected outcome: http://prntscr.com/nz6byp
I already tried setting the width to 100%.
HTML
.left-sidebar{
background-color:#F7F7F7;
padding: 20px;
border-radius: 5px 0px 0px 5px;
}
.searchbox{
padding:20px 10px;
width: 100%;
}
.input-group-btn{
margin: auto;
}
.search-icon{
margin: auto;
font-size: 14px;
background-size: 250%;
background-image: linear-gradient(to right, #77A1D3 0%, #79CBCA 51%, #77A1D3 100%);
transition: background 0.5s ease-out;
color:#fff;
}
.search-icon:hover{
background-position: right center;
color: #fff;
}
.form-control:focus{
border:2px solid #fff;
}
.chat-left-img,.chat-left-detail{
float: left;
}
.left-chat{
overflow-y: scroll;
width: 100%;
}
.left-chat::-webkit-scrollbar-track
{
}
.left-chat::-webkit-scrollbar
{
width: 12px;
background-color: #F5F5F5;
}
.left-chat::-webkit-scrollbar-thumb
{
border-radius: 5px;
/*-webkit-box-shadow: inset 0 0 6px rgba(0,0,0,.3);*/
background-color: #DEDEDE;
}
.left-chat ul{
overflow: hidden;
padding: 0px;
}
.left-chat ul li{
list-style: none;
width:100%;
float: left;
padding: 5px;
margin: auto;
background-color: #F2F2F2;
border-radius: 0px;
transition: background 0.25s ease-out;
}
.left-chat ul li:hover{
background-color: #E2E2E2
}
.chat-left-img img{
width:50px;
height:50px;
border-radius: 50%;
text-align: left;
float:fixed;
padding: 3px;
background: linear-gradient(to right, #77A1D3 0%, #79CBCA 51%, #77A1D3 100%);
background-size: 250%;
}
.chat-left-details{
width: 100%;
}
.chat-left-details a{
margin: 5%;
text-decoration: none;
color: #5D5C5C;
font-weight: 200;
}
.online{
margin: 5%;
color:#86BB71;
font-size: 14px;
}
.offline{
margin: 5%;
color:#C6C4C4;
font-size: 14px;
}
<div class="col-md-3 col-sm-3 col-cs-12 left-sidebar">
<div class="input-group searchbox">
<div class="input-group-btn">
<center><button id="" class="btn btn-default search-icon" name="search_user" type="submit">Add new user</button></center>
</div>
</div>
<div class="left-chat">
<ul>
<li>
<div class='chat-left-img'> <img src='$user_profilepic'>
</div>
<div class='chat-left-details'>
<a href='home.php?user_name=$user_name'>$user_name</a>
<span style='font-size: 12px; color: #5D5C5C;'>(You)
</span><br>
</div>
</li>
</ul>
</div>
Any help is appreciated!

Answer 1

The list elements' width is set to 100% of container, but container has padding, thats why you think it's not filled the container.
.left-sidebar has padding: 20px;, and also .left-chat has overflow-y: scroll. these two rules makes element smaller than you expect (some for parent padding, some for scrollbar width).
you can padding: 0 for .left-sidebar and set overflow-y: auto for .left-chat.
Also you can inspect elements on chrome dev tools, to see whats going on.
you can see this here: codepen

Answer 2

Your .left-sidebar has a 20px padding.
I removed left and right padding and now the list take full width
.left-sidebar{
background-color:#F7F7F7;
padding: 20px;
border-radius: 5px 0px 0px 5px;
}
.left-sidebar{
background-color:#F7F7F7;
padding: 20px 0;
border-radius: 5px 0 0 5px;
}
.searchbox{
padding:20px 10px;
width: 100%;
}
.input-group-btn{
margin: auto;
}
.search-icon{
margin: auto;
font-size: 14px;
background-size: 250%;
background-image: linear-gradient(to right, #77A1D3 0%, #79CBCA 51%, #77A1D3 100%);
transition: background 0.5s ease-out;
color:#fff;
}
.search-icon:hover{
background-position: right center;
color: #fff;
}
.form-control:focus{
border:2px solid #fff;
}
.chat-left-img,.chat-left-detail{
float: left;
}
.left-chat{
overflow-y: auto;
width: 100%;
}
.left-chat::-webkit-scrollbar
{
width: 12px;
background-color: #F5F5F5;
}
.left-chat::-webkit-scrollbar-thumb
{
border-radius: 5px;
/*-webkit-box-shadow: inset 0 0 6px rgba(0,0,0,.3);*/
background-color: #DEDEDE;
}
.left-chat ul{
overflow: hidden;
padding: 0px;
}
.left-chat ul li{
list-style: none;
width:100%;
float: left;
padding: 5px;
background-color: #F2F2F2;
border-radius: 0px;
transition: background 0.25s ease-out;
}
.left-chat ul li:hover{
background-color: #E2E2E2
}
.chat-left-img img{
width:50px;
height:50px;
border-radius: 50%;
text-align: left;
float:fixed;
padding: 3px;
background: linear-gradient(to right, #77A1D3 0%, #79CBCA 51%, #77A1D3 100%);
background-size: 250%;
}
.chat-left-details{
width: 100%;
}
.chat-left-details a{
margin: 5%;
text-decoration: none;
color: #5D5C5C;
font-weight: 200;
}
<div class="col-md-3 col-sm-3 col-cs-12 left-sidebar">
<div class="input-group searchbox">
<div class="input-group-btn">
<center><button id="" class="btn btn-default search-icon" name="search_user" type="submit">Add new user</button></center>
</div>
</div>
<div class="left-chat">
<ul class="full-width-no-padding">
<li class="full-width-no-padding">
<div class='chat-left-img'> <img src='$user_profilepic'>
</div>
<div class='chat-left-details'>
<a href='home.php?user_name=$user_name'>$user_name</a>
<span style='font-size: 12px; color: #5D5C5C;'>(You)
</span><br>
</div>
</li>
</ul>
</div>
EDIT
As #yaya pro suggested i added overflow-y: auto; to .left-chat class