💄 Finished the common style settings.

assets/css/_common/scaffolding/base.scss

@@ -0,0 +1,99 @@
+::selection {
+  background: $selection-bg;
+  color: $selection-color;
+}
+
+html, body {
+  height: 100%;
+}
+
+body {
+  background: var(--body-bg-color);
+  box-sizing: border-box;
+  color: var(--text-color);
+  font-family: $font-family-base;
+  font-size: $font-size-base;
+  line-height: $line-height-base;
+  min-height: 100%;
+  position: relative;
+  transition: padding $transition-ease;
+
+  @if $cfg_bd_scrollbar_overlay {
+    overflow-x: hidden;
+    @supports (overflow-x: clip) {
+      overflow-x: clip;
+    }
+    width: 100vw;
+  }
+
+  @if $cfg_bd_scrollbar_stable {
+    overflow-y: scroll;
+  }
+}
+
+h1, h2, h3, h4, h5, h6 {
+  font-family: $font-family-headings;
+  font-weight: bold;
+  line-height: 1.5;
+  margin: 30px 0 15px;
+}
+
+@for $headline from 1 through 6 {
+  h#{$headline} {
+    font-size: $font-size-headings-base - $font-size-headings-step * $headline;
+  }
+}
+
+p {
+  margin: 0 0 20px;
+}
+
+a {
+  border-bottom: 1px solid $link-decoration-color;
+  color: var(--link-color);
+  // For a:not(:any-link)
+  cursor: pointer;
+  outline: 0;
+  text-decoration: none;
+  @include word-wrap();
+
+  &:hover {
+    border-bottom-color: var(--link-hover-color);
+    color: var(--link-hover-color);
+  }
+}
+
+iframe, img, video, embed {
+  display: block;
+  margin-left: auto;
+  margin-right: auto;
+  max-width: 100%;
+}
+
+hr {
+  background-image: repeating-linear-gradient(-45deg, $grey-lighter, $grey-lighter 4px, transparent 4px, transparent 8px);
+  border: 0;
+  height: 3px;
+  margin: 40px 0;
+}
+
+blockquote {
+  border-left: 4px solid $grey-lighter;
+  color: var(--blockquote-color);
+  margin: 0;
+  padding: 0 15px;
+
+  cite::before {
+    content: '-';
+    padding: 0 5px;
+  }
+}
+
+dt {
+  font-weight: bold;
+}
+
+dd {
+  margin: 0;
+  padding: 0;
+}