<ol class="periodic-table">
<li class="hydrogen">
    <abbr title="Hydrogen">H</abbr>
</li>
<li id="helium" class="noble-gas">
    <abbr title="Helium">He</abbr>
    <span>2</span>
</li>
<li class="alkali">
    <abbr title="Lithium">Li</abbr>
</li>
<li class="alkaline">
    <abbr title="Beryllium">Be</abbr>
</li>
<li id="boron" class="metalloid">
    <abbr title="Boron">B</abbr>
</li>
<li class="polyatomic-non-metal">
    <abbr title="Carbon">C</abbr>
</li>
<li class="diatomic-nonmetal">
    <abbr title="Nitrogen">N</abbr>
</li>
<li class="diatomic-nonmetal">
    <abbr title="Oxygen">O</abbr>
</li>
<li class="diatomic-nonmetal">
    <abbr title="Fluorine">F</abbr>
</li>
<li class="noble-gas">
    <abbr title="Neon">Ne</abbr>
</li>
<li class="alkali">
    <abbr title="Sodium">Na</abbr>
</li>
<li class="alkaline">
    <abbr title="Magnesium">Mg</abbr>
</li>
<li id="aluminium">
    <abbr title="Aluminium">Al</abbr>
</li>
<li class="metalloid">
    <abbr title="Silicon">Si</abbr>
</li>
<li class="polyatomic-non-metal">
    <abbr title="Phosphorus">P</abbr>
</li>
<li class="polyatomic-non-metal">
    <abbr title="Sulphur">S</abbr>
</li>
<li class="diatomic-nonmetal">
    <abbr title="Chlorine">Cl</abbr>
</li>
<li class="noble-gas">
    <abbr title="Argon">Ar</abbr>
</li>
<li class="alkali">
    <abbr title="Potassium">K</abbr>
</li>
<li class="alkaline">
    <abbr title="Calcium">Ca</abbr>
</li>
<li>
    <abbr title="Scandium">Sc</abbr>
</li>
<li>
    <abbr title="Titanium">Ti</abbr>
</li>
<li>
    <abbr title="Vanadium">Ti</abbr>
</li>
<li>
    <abbr title="Chromium">Cr</abbr>
</li>
<li>
    <abbr title="Manganese">Mn</abbr>
</li>
<li>
    <abbr title="Iron">Fe</abbr>
</li>
<li>
    <abbr title="Cobalt">Co</abbr>
</li>
<li>
    <abbr title="Nickel">Ni</abbr>
</li>
<li>
    <abbr title="Copper">Cu</abbr>
</li>
<li>
    <abbr title="Zinc">Zn</abbr>
</li>
<li>
    <abbr title="Gallium">Ga</abbr>
</li>
<li class="metalloid">
    <abbr title="Germanium">Ge</abbr>
</li>
<li class="metalloid">
    <abbr title="Arsenic">As</abbr>
</li>
<li class="polyatomic-non-metal">
    <abbr title="Selenium">Se</abbr>
</li>
<li class="diatomic-nonmetal">
    <abbr title="Bromide">Br</abbr>
</li>
<li class="noble-gas">
    <abbr title="Krypton">Kr</abbr>
</li>
<li class="alkali">
    <abbr title="Rubidium">Rb</abbr>
</li>
<li class="alkaline">
    <abbr title="Strontium">Sr</abbr>
</li>
<li>
    <abbr title="Yttrium">Y</abbr>
</li>
<li>
    <abbr title="Zirconium">Zr</abbr>
</li>
<li>
    <abbr title="Niobium">Nb</abbr>
</li>
<li>
    <abbr title="Molybdenum">Mo</abbr>
</li>
<li>
    <abbr title="Technetium">Tc</abbr>
</li>
<li>
    <abbr title="Ruthenium">Ru</abbr>
</li>
<li>
    <abbr title="Rhodium">Ro</abbr>
</li>
<li>
    <abbr title="Palladium">Pd</abbr>
</li>
<li>
    <abbr title="Silver">Ag</abbr>
</li>
<li>
    <abbr title="Cadmium">Cd</abbr>
</li>
<li>
    <abbr title="Indium">In</abbr>
</li>
<li>
    <abbr title="Tin">Sn</abbr>
</li>
<li class="metalloid">
    <abbr title="Antimony">Sb</abbr>
</li>
<li class="metalloid">
    <abbr title="Tellurium">Te</abbr>
</li>
<li class="diatomic-nonmetal">
    <abbr title="Iodine">I</abbr>
</li>
<li class="noble-gas">
    <abbr title="Xenon">Xe</abbr>
</li>
<li class="alkali">
    <abbr title="Caesium">Cs</abbr>
</li>
<li class="alkaline">
    <abbr title="Barium">Ba</abbr>
</li>
<li class="lanthanide">
    <abbr title="Lanthanum">La</abbr>
</li>
<li id="cerium" class="lanthanide">
     <abbr title="Cerium">Ce</abbr>
</li>
<li class="lanthanide">
    <abbr title="Praseodymium">Pr</abbr>
</li>
<li class="lanthanide">
    <abbr title="Neodymium">Nd</abbr>
</li>
<li class="lanthanide">
    <abbr title="Promethium">Pm</abbr>
</li>
<li class="lanthanide">
    <abbr title="Samarium">Sm</abbr>
</li>
<li class="lanthanide">
    <abbr title="Europium">Eu</abbr>
</li>
<li class="lanthanide">
    <abbr title="Gadolinium">Gd</abbr>
</li>
<li class="lanthanide">
    <abbr title="Terbium">Td</abbr>
</li>
<li class="lanthanide">
    <abbr title="Dysprosium">Dy</abbr>
</li>
<li class="lanthanide">
    <abbr title="Holmium">Ho</abbr>
</li>
<li class="lanthanide">
    <abbr title="Erbium">Er</abbr>
</li>
<li class="lanthanide">
    <abbr title="Thulium">Tm</abbr>
</li>
<li class="lanthanide">
    <abbr title="Ytterbium">Yb</abbr>
</li>
<li class="lanthanide">
    <abbr title="Lutetium">Lu</abbr>
</li>  
<li id="hafnium">
    <abbr title="Hafnium">Hf</abbr>
</li>
<li>
    <abbr title="Tantalum">Ta</abbr>
</li>
<li>
    <abbr title="Tungsten">W</abbr>
</li>
<li>
    <abbr title="Rhenium">Re</abbr>
</li>
<li>
    <abbr title="Osmium">Os</abbr>
</li> 
<li>
    <abbr title="Iridium">Ir</abbr>
</li>
<li>
    <abbr title="Platinum">Pt</abbr>
</li>
<li>
    <abbr title="Gold">Au</abbr>
</li>
<li>
    <abbr title="Mercury">Hg</abbr>
</li>
<li>
    <abbr title="Thallium">Tl</abbr>
</li>
<li>
    <abbr title="Lead">Pb</abbr>
</li>
<li>
    <abbr title="Bismuth">Bi</abbr>
</li>
<li>
    <abbr title="Polonium">Po</abbr>
</li>
<li class="metalloid">
    <abbr title="Astatine">At</abbr>
</li>
<li class="noble-gas">
    <abbr title="Radon">Rn</abbr>
</li>
<li class="alkali">
    <abbr title="Francium">Fr</abbr>
</li>
<li class="alkaline">
    <abbr title="Radium">Ra</abbr>
</li>
<li class="actinide">
    <abbr title="Actinium">Ac</abbr>
</li>
<li class="actinide" id="thorium" >
    <abbr title="Thorium">Th</abbr>
</li>
<li class="actinide">
    <abbr title="Protactinium">Pa</abbr>
</li>
<li class="actinide">
    <abbr title="Uranium">U</abbr>
</li>
<li class="actinide">
    <abbr title="Neptunium">Np</abbr>
</li>
<li class="actinide">
    <abbr title="Plutonium">Up</abbr>
</li>
<li class="actinide">
    <abbr title="Americium">Am</abbr>
</li>
<li class="actinide">
    <abbr title="Curium">Cm</abbr>
</li>
<li class="actinide">
    <abbr title="Berkelium">Bk</abbr>
</li>
<li class="actinide">
    <abbr title="Californium">Cf</abbr>
</li>
<li class="actinide">
    <abbr title="Einsteinium">Es</abbr>
</li>
<li class="actinide">
    <abbr title="Fermium">Fm</abbr>
</li>
<li class="actinide">
    <abbr title="Mendelevium">Md</abbr>
</li>
<li class="actinide">
    <abbr title="Nobelium">No</abbr>
</li>
<li class="actinide">
    <abbr title="Lawrencium">Lr</abbr>
</li>
<li id="rutherfordium">
    <abbr title="Rutherfordium">Rf</abbr>
</li>
<li>
    <abbr title="Dubnium">Db</abbr>
</li>
<li>
    <abbr title="Seaborgium">Sg</abbr>
</li>
<li>
    <abbr title="Bohrium">Bh</abbr>
</li>
<li>
    <abbr title="Hassium">Hs</abbr>
</li>
<li class="unknown">
    <abbr title="Meitnerium">Mt</abbr>
</li>
<li class="unknown">
    <abbr title="Darmstadtium">Ds</abbr>
</li>
<li class="unknown">
    <abbr title="Roentgenium">Rg</abbr>
</li>
<li>
    <abbr title="Copernicium">Cn</abbr>
</li>
<li class="unknown">
    <abbr title="Nihonium">Cn</abbr>
</li>
<li class="unknown">
    <abbr title="Flerovium">Fl</abbr>
</li>
<li class="unknown">
    <abbr title="Moscovium">Mc</abbr>
</li>
<li class="unknown">
    <abbr title="Livermorium">Lv</abbr>
</li>
<li class="unknown">
    <abbr title="Tennessine">Ts</abbr>
</li>
<li class="unknown">
    <abbr title="Oganesson">Og</abbr>
</li>
</ol>

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  font-weight: normal;
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* {
  box-sizing: border-box;
}
body {
  font-family: Phenomena, script;
  margin: 5vw;
  background: #111;
  color: #000;
  counter-reset: element;
}
.periodic-table {
  display: grid;
  grid-column-gap: .5vw;
  grid-row-gap: .5vw;
  padding-left: 0;
}
.periodic-table > li {
  display: flex;
  position: relative;
  justify-content: center;
  align-items: center;
  height: 4.5vw;
  border-radius: 3px;
  background: rgb(91, 194, 234);
  font-weight: bold;
}
.periodic-table > li:before {
  counter-increment: element; 
  content: counter(element);
  position: absolute;
  bottom: 5px;
  left: 6px;
  font-size: .9vw;
  font-weight: lighter;
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.periodic-table > li abbr {
  font-size: 2.5vw;
}
#helium {
  grid-column-start: 18;
}
#boron, #aluminium {
  grid-column-start: 13;
}
#cerium, #thorium {
  grid-column-start: 4;
}
.periodic-table > li:nth-child(n+58):nth-last-child(n+48) {
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.periodic-table > li:nth-child(n+90):nth-last-child(n+16) {
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.periodic-table:before {
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  content: '';
  grid-row: 8 / 10;
  grid-column: 1 / 4;
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.periodic-table .noble-gas {
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}
.periodic-table .diatomic-nonmetal {
  background: rgb(234, 179, 127);
}
.periodic-table .alkali {
  background: hsl(326, 52%, 84%);
}
.periodic-table .hydrogen {
  background: rgb(163, 199, 210);  
}
.periodic-table .alkaline {
  background: hsl(120, 52%, 84%);
}
.periodic-table .unknown {
  background: hsl(210, 2%, 73%);
}
.periodic-table .lanthanide {
  background: hsl(183, 54%, 84%);
}
.periodic-table .actinide {
  background: hsl(82, 60%, 56%);  
}
.periodic-table .metalloid {
  background: hsl(142, 60%, 56%);  
}
.periodic-table .polyatomic-non-metal {
  background: hsl(358, 60%, 56%);  
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@media all and (max-width: 1100px) {
  #helium, #boron, #aluminium, #cerium, #thorium {
  grid-column-start: auto;
  }
  .periodic-table {
  grid-template-columns: 1fr 1fr 1fr;
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  .periodic-table > li abbr {
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  .periodic-table > li {
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  .periodic-table > li:before {
    font-size: 1rem;
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  .periodic-table > li:nth-child(n+58):nth-last-child(n+48) {
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}
  .periodic-table > li:nth-child(n+90):nth-last-child(n+16) {
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  .periodic-table:before {
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}
@media all and (max-width: 750px) {
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  .periodic-table {
    grid-template-columns: 1fr 1fr;
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  .periodic-table > li {
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    font-size: 3vw;
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}
@media all and (max-width: 550px) {
  .periodic-table {
    grid-template-columns: 1fr;
  }
}

// A few notes of things that might not be immediately apparent from reading the CSS spec:

// placing a grid child element at a grid-column-start position (Helium, for example), automatically creates that number of columns: 18, in this case

// subsequent child elements "flow" from that new point automatically

// I've set the height of the elements using vw units, but it could be more accurately determined using calc