--- /dev/null
+figure:before {
+ content: '';
+ position: absolute;
+ width: 100%;
+ height: 100%;
+}
+.parent > figure:after {
+ position: absolute;
+ right: 0;
+ content: '+';
+ color: #FFF;
+ background: #0008;
+ border-radius: 1em;
+ padding: 0 .2em;
+}
+figure .debug {
+ position: absolute;
+ left: .1em;
+}
+
+/* essential = transparent white */
+.level0 > figure:before {
+ box-shadow: inset 0 0 2em #FFF;
+}
+
+/* ubiquitous = cyan */
+.level1 > figure:before {
+ box-shadow: inset 0 0 1em #0FF;
+}
+.level1 > figure figcaption {
+ background: #8FFA;
+}
+
+/* basic = green */
+.level2 > figure {
+ filter: hue-rotate(-70deg) sepia(.4) hue-rotate(70deg) saturate(2);
+}
+.level2 > figure:before {
+ box-shadow: inset 0 0 1em #6FA;
+}
+.level2 > figure figcaption {
+ background: #AFDC;
+}
+
+/* common = lime */
+.level3 > figure {
+ filter: hue-rotate(-45deg) sepia(.6) hue-rotate(45deg) saturate(2);
+}
+.level3 > figure:before {
+ box-shadow: inset 0 0 1em #2F0;
+}
+.level3 > figure figcaption {
+ background: #8F8C;
+}
+
+/* distinctive = yellow */
+.level4 > figure {
+ filter: hue-rotate(-15deg) sepia(.7) hue-rotate(15deg) saturate(2);
+}
+.level4 > figure:before {
+ box-shadow: inset 0 0 1em #FD0;
+}
+.level4 > figure figcaption {
+ background: #FE8C;
+}
+
+/* specialised = orange */
+.level5 > figure {
+ filter: hue-rotate(10deg) sepia(.8) hue-rotate(-10deg) saturate(2);
+}
+.level5 > figure:before {
+ box-shadow: inset 0 0 2em #F80;
+}
+.level5 > figure figcaption {
+ background: #FC8C;
+}
+
+/* rare = red */
+.level6 > figure {
+ filter: hue-rotate(40deg) sepia(.9) hue-rotate(-40deg) saturate(2);
+}
+.level6 > figure:before {
+ box-shadow: inset 0 0 3em #F00;
+}
+.level6 > figure figcaption {
+ background: #F88C;
+}
+
+/* invisible = grey */
+.level7 > figure {
+ filter: sepia(.9) hue-rotate(-60deg);
+}
+.level7 > figure:before {
+ box-shadow: inset 0 0 3em #804;
+}
+.level7 > figure figcaption {
+ background: #C68C;
+}