Untitled

dabblet.css

body { font-size: 250px; }
.responsive-number { white-space: nowrap; }
.responsive-number > *:before { content: " "; /* six-per-em-space */ }
.responsive-number > :first-child:before {content: ""; }
@media (max-width: 1000px) {
  .m-group:after { content: " M"; }
  .k-group, .base-group { display: none; }
}
@media (max-width: 1300px) {
  .k-group:after { content: " k"; }
  .base-group { display: none; }
}

dabblet.html

<span class="responsive-number"><span class="m-group">123</span><span class="k-group">456</span><span class="base-group">789</span></span>

settings.json

{"view":"split","fontsize":"100","seethrough":"","prefixfree":"","page":"all"}