style.css

*, *:before, *:after {
    box-sizing: border-box;
}

:root {
    --white: #fff;
    --black: #000;
    --bg: #f8f8f8;
    --grey: #999;
    --dark: #1a1a1a;
    --light: #e6e6e6;
    --wrapper: 1000px;
    --blue: #00b0ff;
}

body {
    background-color: var(--bg);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    text-rendering: optimizeLegibility;
    font-family: 'Source Sans Pro', sans-serif;
    font-weight: 400;
    background-image: url("https://s3-us-west-2.amazonaws.com/s.cdpn.io/382994/image.jpg");
    background-size: cover;
    background-repeat: none;
}

ul,li{
  margin:0;
  padding:0;
  list-style-type: none
}

.wrapper {
    position: relative;
    left: 50%;
    width: var(--wrapper);
    height: 800px;
    -webkit-transform: translate(-50%, 0);
    transform: translate(-50%, 0);
}

.container {
    position: relative;
    top: 50%;
    left: 50%;
    width: 80%;
    height: 75%;
    background-color: var(--white);
    -webkit-transform: translate(-50%, -50%);
    transform: translate(-50%, -50%);
}
.container .left {
    float: left;
    width: 37.6%;
    height: 100%;
    border: 1px solid var(--light);
    background-color: var(--white);
}
.container .left .top {
    position: relative;
    width: 100%;
    height: 96px;
    padding: 29px;
}
.container .left .top:after {
    position: absolute;
    bottom: 0;
    left: 50%;
    display: block;
    width: 80%;
    height: 1px;
    content: '';
    background-color: var(--light);
    -webkit-transform: translate(-50%, 0);
    transform: translate(-50%, 0);
}
.container .left input {
    float: left;
    width: 188px;
    height: 42px;
    padding: 0 15px;
    border: 1px solid var(--light);
    background-color: #eceff1;
    border-radius: 21px;
    font-family: 'Source Sans Pro', sans-serif;
    font-weight: 400;
}
.container .left input:focus {
    outline: none;
}
.container .left a.search {
    display: block;
    float: left;
    width: 42px;
    height: 42px;
    margin-left: 10px;
    border: 1px solid var(--light);
    background-color: var(--blue);
    background-image: url("https://s3-us-west-2.amazonaws.com/s.cdpn.io/382994/name-type.png");
    background-repeat: no-repeat;
    background-position: top 12px left 14px;
    border-radius: 50%;
}
.container .left .people {
    margin-left: -1px;
    border-right: 1px solid var(--light);
    border-left: 1px solid var(--light);
    width: calc(100% + 2px);
    height: calc(76% + 1px);
    overflow:scroll;
}
.container .left .people .person {
    position: relative;
    width: 100%;
    padding: 12px 10% 16px;
    cursor: pointer;
    background-color: var(--white);
}

.container .left .people .person:after {
    position: absolute;
    bottom: 0;
    left: 50%;
    display: block;
    width: 80%;
    height: 1px;
    content: '';
    background-color: var(--light);
    -webkit-transform: translate(-50%, 0);
    transform: translate(-50%, 0);
}
.container .left .people .person img {
    float: left;
    width: 40px;
    height: 40px;
    margin-right: 12px;
    border-radius: 50%;
}
.container .left .people .person .name {
    font-size: 14px;
    line-height: 22px;
    color: var(--dark);
    font-family: 'Source Sans Pro', sans-serif;
    font-weight: 600;
    display: block;
}
.container .left .people .person .time {
    font-size: 14px;
    position: absolute;
    top: 16px;
    right: 10%;
    padding: 0 0 5px 5px;
    color: var(--grey);
    background-color: var(--white);
}
.container .left .people .person .preview {
    font-size: 14px;
    display: inline-block;
    overflow: hidden !important;
    width: 70%;
    white-space: nowrap;
    text-overflow: ellipsis;
    color: var(--grey);
}
.container .left .people .person.active, .container .left .people .person:hover {
    margin-top: -1px;
    margin-left: -1px;
    padding-top: 13px;
    border: 0;
    background-color: #eceff1;
    width: calc(100% + 2px);
    padding-left: calc(10% + 1px);
}
.container .left .people .person.active span, .container .left .people .person:hover span {
    background: transparent;
}
.container .left .people .person.active:after, .container .left .people .person:hover:after {
    display: none;
}
.container .right {
    position: relative;
    float: left;
    width: 62.4%;
    height: 100%;
}
.container .right .top {
    width: 100%;
    height: 47px;
    padding: 15px 29px;
    background-color: #eceff1;
}
.container .right .top span {
    font-size: 15px;
    color: var(--grey);
}
.container .right .top span .name {
    color: var(--dark);
    font-family: 'Source Sans Pro', sans-serif;
    font-weight: 600;
}
.container .right .chat {
    position: relative;
    display: none;
    overflow: hidden;
    padding: 0 35px 92px;
    border-width: 1px 1px 1px 0;
    border-style: solid;
    border-color: var(--light);
    height: calc(100% - 48px);
    justify-content: flex-end;
    flex-direction: column;
}
.container .right .chat.active-chat {
    display: block;
    display: flex;
}
.container .right .chat.active-chat .bubble {
    transition-timing-function: cubic-bezier(0.4, -0.04, 1, 1);
}
.container .right .chat.active-chat .bubble:nth-of-type(1) {
    -webkit-animation-duration: 0.15s;
    animation-duration: 0.15s;
}
.container .right .chat.active-chat .bubble:nth-of-type(2) {
    -webkit-animation-duration: 0.3s;
    animation-duration: 0.3s;
}
.container .right .chat.active-chat .bubble:nth-of-type(3) {
    -webkit-animation-duration: 0.45s;
    animation-duration: 0.45s;
}
.container .right .chat.active-chat .bubble:nth-of-type(4) {
    -webkit-animation-duration: 0.6s;
    animation-duration: 0.6s;
}
.container .right .chat.active-chat .bubble:nth-of-type(5) {
    -webkit-animation-duration: 0.75s;
    animation-duration: 0.75s;
}
.container .right .chat.active-chat .bubble:nth-of-type(6) {
    -webkit-animation-duration: 0.9s;
    animation-duration: 0.9s;
}
.container .right .chat.active-chat .bubble:nth-of-type(7) {
    -webkit-animation-duration: 1.05s;
    animation-duration: 1.05s;
}
.container .right .chat.active-chat .bubble:nth-of-type(8) {
    -webkit-animation-duration: 1.2s;
    animation-duration: 1.2s;
}
.container .right .chat.active-chat .bubble:nth-of-type(9) {
    -webkit-animation-duration: 1.35s;
    animation-duration: 1.35s;
}
.container .right .chat.active-chat .bubble:nth-of-type(10) {
    -webkit-animation-duration: 1.5s;
    animation-duration: 1.5s;
}

.container .right .chat.active-chat .bubble span{
    font-size:11px;
    display: block;
    text-align: right;
}

.container .right .write {
    position: absolute;
    bottom: 29px;
    left: 30px;
    height: 42px;
    padding-left: 8px;
    border: 1px solid var(--light);
    background-color: #eceff1;
    width: calc(100% - 58px);
    border-radius: 5px;
}
.container .right .write input {
    font-size: 16px;
    float: left;
    width: 347px;
    height: 40px;
    padding: 0 10px;
    color: var(--dark);
    border: 0;
    outline: none;
    background-color: #eceff1;
    font-family: 'Source Sans Pro', sans-serif;
    font-weight: 400;
}
.container .right .write .write-link.attach:before {
    display: inline-block;
    float: left;
    width: 20px;
    height: 42px;
    content: '';
    background-image: url("https://s3-us-west-2.amazonaws.com/s.cdpn.io/382994/attachment.png");
    background-repeat: no-repeat;
    background-position: center;
}
.container .right .write .write-link.smiley:before {
    display: inline-block;
    float: left;
    width: 20px;
    height: 42px;
    content: '';
    background-image: url("https://s3-us-west-2.amazonaws.com/s.cdpn.io/382994/smiley.png");
    background-repeat: no-repeat;
    background-position: center;
}
.container .right .write .write-link.send:before {
    display: inline-block;
    float: left;
    width: 20px;
    height: 42px;
    margin-left: 45px;
    content: '';
    background-image: url("https://s3-us-west-2.amazonaws.com/s.cdpn.io/382994/send.png");
    background-repeat: no-repeat;
    background-position: center;
}
.container .right .bubble {
    font-size: 16px;
    position: relative;
    display: inline-block;
    clear: both;
    margin-bottom: 8px;
    padding: 6px 14px;
    vertical-align: top;
    border-radius: 5px;
    min-width: 121px;
}
.container .right .bubble:before {
    position: absolute;
    top: 19px;
    display: block;
    width: 8px;
    height: 6px;
    content: '\00a0';
    -webkit-transform: rotate(29deg) skew(-35deg);
    transform: rotate(29deg) skew(-35deg);
}
.container .right .bubble.you {
    float: left;
    color: var(--white);
    background-color: var(--blue);
    align-self: flex-start;
    -webkit-animation-name: slideFromLeft;
    animation-name: slideFromLeft;
}
.container .right .bubble.you:before {
    left: -3px;
    background-color: var(--blue);
}
.container .right .bubble.me {
    float: right;
    color: var(--dark);
    background-color: #eceff1;
    align-self: flex-end;
    -webkit-animation-name: slideFromRight;
    animation-name: slideFromRight;
}
.container .right .bubble.me:before {
    right: -3px;
    background-color: #eceff1;
}
.container .right .conversation-start {
    position: relative;
    width: 100%;
    margin-bottom: 27px;
    text-align: center;
}
.container .right .conversation-start span {
    font-size: 14px;
    display: inline-block;
    color: var(--grey);
}
.container .right .conversation-start span:before, .container .right .conversation-start span:after {
    position: absolute;
    top: 10px;
    display: inline-block;
    width: 30%;
    height: 1px;
    content: '';
    background-color: var(--light);
}
.container .right .conversation-start span:before {
    left: 0;
}
.container .right .conversation-start span:after {
    right: 0;
}

.tab{

}

.tab li{
    width: 50%;
    float: left;
}
.tab li a{
    height:40px;
    display: block;
    text-align: center;
    color: black;
    background: #fafafa;
    text-decoration: none;
    padding: 10px;
    font-size: 15px;
}
.tab li a.active, .tab li a:hover{
    background: #eceff1;
}

.bottom{
    text-align: center;
    padding-top: 16px
}

@keyframes slideFromLeft {
    0% {
        margin-left: -200px;
        opacity: 0;
    }
    100% {
        margin-left: 0;
        opacity: 1;
    }
}
@-webkit-keyframes slideFromLeft {
    0% {
        margin-left: -200px;
        opacity: 0;
    }
    100% {
        margin-left: 0;
        opacity: 1;
    }
}
@keyframes slideFromRight {
    0% {
        margin-right: -200px;
        opacity: 0;
    }
    100% {
        margin-right: 0;
        opacity: 1;
    }
}
@-webkit-keyframes slideFromRight {
    0% {
        margin-right: -200px;
        opacity: 0;
    }
    100% {
        margin-right: 0;
        opacity: 1;
    }
}