a:hover {
    background-color: yellow;
}
span:hover {
    background-color: yellow;
}

body {
    background: white
    }
P.blocktext {
    margin-left: auto;
    margin-right: auto;
    width: 55%
    }
TABLE.chart {
    margin-left: auto;
    margin-right: auto;
    }
H1 {
    text-align: center;
    }
H2 {
    text-align: center;
    }
H3 {
    text-align: center;
    }
H4 {
    text-align: center;
    }
H5 {
    text-align: center;
    }
UL {
    margin-left: auto;
    margin-right: auto;
    width: 55%
    }
OL {
    margin-left: auto;
    margin-right: auto;
    width: 55%
    }
IMG {
    display: block;
    margin-left: auto;
    margin-right: auto
    }
IFRAME.youtube-player {
    display: block;
    margin-left: auto;
    margin-right: auto
    }