body
{
    display: flex;
    flex-direction: column;
    background-color:#fff;
    margin: 8px;
}
#header
{
    display: flex;
    flex-direction: row;
    justify-content: center;
    align-content: center;
    margin-bottom: 4px;
}
.header_element
{
    display: flex;
    justify-content: center;
    flex: 1;
    background-color: rgba(0, 0, 0, 0.1);   
}
.header_element:hover
{
    background-color: rgba(0, 0, 0, 0.2);
}
.hidden
{
    display: none;
}
#content_body
{
    flex: 0 0 auto;
    display: flex;
    flex-direction: row;
}