web-base--/simple-demo/toc/h.css

body {
    counter-reset: h1-count h2-count h3-count h4-count h5-count h6-count;
}

.t h1 {
    counter-reset: h2-count 0;
}

.t h2 {
    counter-reset: h3-count 0;
}

.t h3 {
    counter-reset: h4-count 0;
}

.t h4 {
    counter-reset: h5-count 0;
}

.t h5 {
    counter-reset: h6-count 0;
}

.t h1:before {
    display: block;
    float: left;
    font-size: 100%;
    counter-increment: h1-count;
    content: "C" counter(h1-count) "\00A0";
}

.t h2:before {
    display: block;
    float: left;
    font-size: 100%;
    counter-increment: h2-count;
    content: counter(h2-count) "\00A0";
}

.t h3:before {
    display: block;
    float: left;
    font-size: 100%;
    counter-increment: h3-count;
    content: counter(h2-count) "." counter(h3-count) "\00A0";
}

.t h4:before {
    display: block;
    float: left;
    font-size: 100%;
    counter-increment: h4-count;
    content: counter(h2-count) "." counter(h3-count) "." counter(h4-count) "\00A0";
}

.t h5:before {
    display: block;
    float: left;
    font-size: 50%;
    counter-increment: h5-count;
    content: counter(h2-count) "." counter(h3-count) "." counter(h4-count) "." counter(h5-count) "\00A0";
}

.t h6:before {
    display: block;
    float: left;
    font-size: 50%;
    counter-increment: h6-count;
    content: counter(h2-count) "." counter(h3-count) "." counter(h4-count) "." counter(h5-count) "." counter(h6-count) "\00A0";
}