style.css

body { background-color: greenyellow; }
#xat {
    float: left;
    display: -webkit-flex;
    display: flex;
    overflow: auto;
    background-color: white;
    width: 45%;
    height: 450px;
    margin: 0% 0% 0% 20%;
    border-color: black;
    border: solid;
    border-radius: 4px;
    border-width: 2px 2px 2px 2px;    
    padding: 1% 0% 0% 1%;
    text-align: left;
}
#llista {
    float:right;
    display: -webkit-flex;
    display: flex;
    overflow: auto;
    background-color: white;
    width: 6%;
    height: 450px;
    margin: 0% 25% 0% 0%;
    border-color: black;
    border: solid;
    border-radius: 4px;
    border-width: 2px 2px 2px 2px;
    text-align: left;
    padding: 1% 0% 0% 1%;
}
ul {
    padding: 0% 0% 0% 0%;
    list-style-type: none;
    display: inline;
}
p {
    padding: 0;
    margin: 0;
}