.def {
    font-weight: bold;
    text-decoration: underline;
    color: red;
}

/*multiple classes*/
.notebox {
    border: 4px solid #666666;
    padding: 0.5em;
    margin: 0.5em;
    color: blue;
}

    .notebox.warning {
        border-color: orange;
        font-weight: bold;
    }

    .notebox.danger {
        border-color: red;
        font-weight: bold;
        text-decoration: underline;
    }

.danger {
    font-size: x-large;
}



/*id selectors*/
#one {
    background-color: yellow;
    color: blue;
}

.p-class {
    background-color: aqua;
    font-size: x-large;
}

h1#heading {
    color: rebeccapurple;
}

/*Selector Lists*/
.class1,
.class2,
.class3 {
    background-color: brown;
}

.class1 {
    color: aqua;
}

.class2,
.class3 {
    color: yellow;
}