body { background-color: lightblue;
       margin: 0% 5%;
       padding: 0px; }

h1, h2 { background-color: lightseagreen; }

h1 { margin-bottom: 1em; }

h2 { margin-top: 1em; }

h3 { color: darkblue; }

h4 { color: blueviolet; }

.solution {
/*  visibility: hidden; */
/*  visibility: visible; */
}