:root {
  --color-dark:         #1b1b1b;
  --color-darker:       #141414;
  --color-light-blue:   #75AFE9;
  --color-lighter-blue: #89D0F2;
  --color-grey:         #2D3436;
  --color-light-grey:   #636E72;
}

@font-face {
  font-family: OpenSans;
  font-weight: normal;
  src: url(font/OpenSans/OpenSans-Regular.ttf);
}

@font-face {
  font-family: OpenSans;
  font-weight: bold;
  src: url(font/OpenSans/OpenSans-Bold.ttf);
}

@font-face {
  font-family: OpenSans;
  font-weight: normal;
  font-style: italic;
  src: url(font/OpenSans/OpenSans-Italic.ttf);
}

html {
  background-color: var(--color-dark);
  min-height: 100%;
  font-family: OpenSans, sans-serif;
  font-size: 1.1rem;
}

body {
  margin: 0;
}

@media screen and (max-width: 48rem) {
  html {
    font-size: 1.0rem;
  }
}

/*****************************************************************************/
/* header                                                                    */

header {
  display: flex;
  margin-bottom: 20px;
  background-color: #191919;
  padding: 10px;
}

header div {
  margin-right: 30px;
  color: #ccc;
}

a.header-link {
  color: #ccc;
  text-decoration: none;
  font-weight: bold;
}

a.header-link:hover {
  color: #fff;
}

/*****************************************************************************/
/* main                                                                      */

main {
  color: #fafafa;
  line-height: 1.80;
  margin: 2rem auto 1rem;
  max-width: 55rem;
  padding: 1.5rem;
}

/*****************************************************************************/
/* common tags                                                               */

/* link */

a {
  text-decoration: none;
}

a, a:visited {
  color: var(--color-lighter-blue);
}

a:hover, a:focus, a:active {
  color: var(--color-light-blue);
}

/* title */

@font-face {
  font-family: Montserrat, sans-serif;
  font-weight: bold;
  src: url(font/Montserrat/Montserrat-Bold.ttf);
}

h1, h2, h3, h4 {
  margin: 10px 0 5px 0;
  line-height: 1.42;
  font-weight: bold;
  font-family: Montserrat;
  letter-spacing: 0.1rem;
}

h1 {
  margin-top: 0;
  font-size: 2.3rem;
}

h2 { font-size: 2.0rem; }
h3 { font-size: 1.7rem; }
h4 { font-size: 1.5rem; }
h5 { font-size: 1.3rem; }
h6 { font-size: 1.1rem; }

/* code */

@font-face {
  font-family: FiraMono;
  font-weight: normal;
  src: url(font/FiraMono/FiraMono-Regular.ttf);
}

pre, code {
  font-family: FiraMono, "Courier New", monospace;
}

code {
  background-color: var(--color-grey);
  padding: 0.2rem 0.3rem;
  border: 1px solid var(--color-light-grey);
  font-size: 82%;
}

pre {
  padding: 0.5rem;
  line-height: 1.25;
  overflow-x: auto;
}

pre > code {
  border: none;
  font-size: 100%;
  padding: 0;
  line-height: 1.4;
}

pre {
  background-color: var(--color-grey);
}

/* other */

p {
  font-size: 1rem;
  margin: 1.3rem 0;
}


blockquote {
  margin-left: 1rem;
  border-left: 3px solid var(--color-light-grey);
  padding-left: 0.5rem;
}

img, canvas, iframe, video, svg, select, textarea {
  max-width: 100%;
}

hr {
  border: 1px solid var(--color-light-grey);
}

table {
  margin: 20px 10px;
}

table, td, th {
  border-collapse: collapse;
  border: 1px solid var(--color-light-grey);
}

td, th {
  vertical-align: top;
  text-align: left;
  padding: 3px 6px;
}

th {
  font-weight: bold;
  background-color: var(--color-grey);
}