:root{
  --bg-dark: #333;
  --bg-light: #f5f5f5;
  --accent: greenyellow;
  --text-light: #fff;
  --text-dark: #000;
  --header-width: 275px;
  --header-height-vh: 93vh;
  --footer-height-vh: 7vh;
  --container-gap: 20px;
  --libutton-w: 200px;
  --libutton-h: 32px;
  --radius-pill: 16px;
  --radius-card: 10px;
  --shadow: 0 2px 4px rgba(0,0,0,0.1);
  --font-sans: "SF Pro Text", Helvetica, Arial, sans-serif;
}

html, body {
  font-family: var(--font-sans);
  min-height: 100vh;
  margin: 0;
  padding: 0;
  line-height: 1.6;
  display: flex;
  flex-direction: column;
  background-color: var(--bg-dark);
  color: var(--text-light);
  box-sizing: border-box;
}

/* Header */
header {
  background-color: var(--bg-dark);
  color: var(--text-light);
  text-align: center;
  padding: 1rem 0;
}

/* Headings */
header h1,
header h2 {
  margin: 0;
  padding-bottom: 5px;
}

/* Separator */
hr {
  width: 80%;
  margin: 0 auto;
  color: var(--accent);
}

/* Navigation */
nav {
  display: flex;
  justify-content: center;
  align-items: center;
}

nav ul {
  list-style: none;
  padding: 0;
  margin: 0;
}

nav ul li {
  margin: 20px 0;
  text-align: center;
  font-size: large;
}

nav ul li a {
  color: var(--text-light);
  text-decoration: none;
}

nav ul li a:hover {
  color: var(--accent);
}

/* Social buttons */
.social-buttons {
  display: inline-flex;
  gap: 10px;
  align-items: center;
}

.social-buttons a {
  text-decoration: none;
  color: var(--text-light);
  padding: 10px;
  border-radius: 50%;
  display: inline-block;
}

/* LinkedIn button container & style */
.linkedinbuttoncontainer {
  display: flex;
  justify-content: center;
  width: 100%;
}

.libutton{
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 7px;
  text-align: center;
  outline: none;
  text-decoration: none !important;
  color: var(--accent) !important;
  width: var(--libutton-w);
  height: var(--libutton-h);
  border-radius: var(--radius-pill);
  background-color: var(--bg-dark);
  font-family: var(--font-sans);
}

/* Social backgrounds */
.linkedin { background: #0077B5; }
.github   { background: #000080; }
.reddit   { background: #FF4500; }
.instagram{ background: #E4405F; }

.fa:hover { opacity: 0.75; }

/* Layout for main and footer shared defaults */
main {
  flex: 1;
  box-sizing: border-box;
  text-align: center;
  padding: 1rem 2rem;
  background-color: var(--bg-light);
  color: var(--text-dark);
}

footer {
  background-color: var(--bg-dark);
  color: var(--text-light);
  text-align: center;
  padding: 0.5rem 0;
  width: 100%;
  box-sizing: border-box;
}

/* Articles grid defaults */
.container {
  display: grid;
  gap: var(--container-gap);
}

/* Controls */
.filter-search-container {
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 20px;
}

.filter { margin-right: 20px; }
.hidden { display: none; }
.search { display: flex; align-items: center; }
.search button { margin-left: 10px; }

/* Article card */
.article {
  display: block;
  background-color: #fff;
  border: 1px solid #ddd;
  border-radius: var(--radius-card);
  padding: 20px;
  text-align: center;
  text-decoration: none;
  color: var(--text-dark);
  box-shadow: var(--shadow);
  transition: transform 0.2s;
}

.article:hover { transform: scale(1.05); }

.article-header { font-size: 18px; font-weight: bold; }
.article-date   { font-size: 14px; color: #888; }
.article-summary{ font-size: 16px; margin-top: 10px; }

/* Responsive breakpoints */

/* Mobile: up to 800px */
@media screen and (max-width: 800px) {
  nav ul li { display: inline; margin: 0 1rem; font-size: inherit; }
  header { padding-top: 10px; }
  main { padding: 1rem 2rem; }
  footer { padding: 0.5rem 0; position: static; }
  .container { grid-template-columns: repeat(2, 1fr); }
}

/* Tablet & Desktop: 801px — 1799px */
@media screen and (min-width: 801px) and (max-width: 1799px) {
  header {
    position: fixed;
    left: 0;
    top: 0;
    width: var(--header-width);
    height: var(--header-height-vh);
    padding: 1rem 0;
  }

  main {
    margin-left: var(--header-width);
    padding: 30px;
    text-align: center;
  }

  footer {
    position: fixed;
    left: 0;
    bottom: 0;
    width: var(--header-width);
    height: var(--footer-height-vh);
    padding: 1rem 0;
  }

  .container { grid-template-columns: repeat(3, 1fr); }
}

/* Large screens: 1800px and up */
@media screen and (min-width: 1800px) {
  header {
    position: fixed;
    left: 0;
    top: 0;
    width: var(--header-width);
    height: var(--header-height-vh);
    padding: 1rem 0;
  }

  main {
    margin-left: var(--header-width);
    padding: 30px;
    text-align: center;
  }

  footer {
    position: fixed;
    left: 0;
    bottom: 0;
    width: var(--header-width);
    height: var(--footer-height-vh);
    padding: 1rem 0;
  }

  .container { grid-template-columns: repeat(4, 1fr); }
}