:root {
  /* Brand colors */
  --logo-accent: oklch(0.5135 0.1192 277.9155); /* #585EAA */

  /* Light theme colors */
  --light-bg-color: oklch(1 0 none); /* #ffffff */
  --light-text-color: oklch(0.3211 0 none); /* #333333 */
  --light-heading-border-color: oklch(0.9424 0.0046 258.3251); /* #eaecef */
  --light-link-color: var(--logo-accent);
  --light-skill-bg-color: oklch(0.9759 0.0120 247.9494); /* #f1f8ff */
  --light-skill-border-color: oklch(0.9009 0.0492 253.0755); /* #c8e1ff */
  --light-code-bg-color: oklch(0.159 0.009 256.85 / 0.05); /* rgba(27, 31, 35, 0.05) */
  --light-logo: url("/logo-black.svg");
  --light-logo-base: oklch(0.2054 0.0067 0.7687); /* #1A1617 */

  /* Dark theme colors */
  --dark-bg-color: oklch(0.2178 0 none); /* #1a1a1a */
  --dark-text-color: oklch(0.9067 0 none); /* #e0e0e0 */
  --dark-heading-border-color: oklch(0.4091 0 none); /* #4a4a4a */
  --dark-link-color: oklch(0.75 0.12 278); /* Lighter logo-accent for dark mode */
  --dark-skill-bg-color: oklch(0.3291 0.0157 248.3029); /* #2f363d */
  --dark-skill-border-color: oklch(0.4156 0.0190 248.2843); /* #444d56 */
  --dark-code-bg-color: oklch(0.968 0.007 254.63 / 0.05); /* rgba(240, 246, 252, 0.05) */
  --dark-logo: url("/logo-white.svg");
  --dark-logo-base: oklch(1 0 none); /* #ffffff */

  /* Default to light theme */
  --bg-color: var(--light-bg-color);
  --text-color: var(--light-text-color);
  --heading-border-color: var(--light-heading-border-color);
  --link-color: var(--light-link-color);
  --skill-bg-color: var(--light-skill-bg-color);
  --skill-border-color: var(--light-skill-border-color);
  --code-bg-color: var(--light-code-bg-color);
  --logo: var(--light-logo);
  --logo-base: var(--light-logo-base);
}

html {
  scroll-behavior: smooth;
}

/* System preference: dark mode */
@media (prefers-color-scheme: dark) {
  :root {
    --bg-color: var(--dark-bg-color);
    --text-color: var(--dark-text-color);
    --heading-border-color: var(--dark-heading-border-color);
    --link-color: var(--dark-link-color);
    --skill-bg-color: var(--dark-skill-bg-color);
    --skill-border-color: var(--dark-skill-border-color);
    --code-bg-color: var(--dark-code-bg-color);
    --logo: var(--dark-logo);
    --logo-base: var(--dark-logo-base);
  }
}

* {
  box-sizing: border-box;
}

body {
  font-family: "Pretendard Variable", Pretendard, -apple-system, BlinkMacSystemFont, system-ui, "Segoe UI", "Roboto", sans-serif;
  line-height: 1.75;
  color: var(--text-color);
  max-width: 800px;
  margin: 0 auto;
  padding: 20px;
  background-color: var(--bg-color);
  transition: background-color 0.1s ease-in-out, color 0.1s ease-in-out;
}

h1 {
  font-size: 2em;
  font-weight: 700;
  margin-bottom: 0.5em;
  line-height: 1.3;
}

h1 em {
  font-weight: 400;
  font-style: normal;
  opacity: 0.7;
  display: block;
  font-size: 0.6em;
  margin-top: 0.25em;
}

h2 {
  font-size: 1.5em;
  font-weight: 600;
  margin-top: 2em;
  margin-bottom: 0.75em;
  padding-bottom: 0.3em;
  border-bottom: 1px solid var(--heading-border-color);
}

h3 {
  font-size: 1.25em;
  font-weight: 600;
  margin-top: 1.5em;
  margin-bottom: 0.5em;
}

a {
  color: var(--link-color);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

code {
  background-color: var(--code-bg-color);
  border-radius: 3px;
  font-size: 85%;
  margin: 0;
  padding: 0.2em 0.4em;
}

section {
  margin-bottom: 2.5em;
  scroll-margin-top: 5em;
}

section > p {
  margin-top: 0.5em;
  margin-bottom: 1em;
}

dl {
  margin-top: 0.75em;
}

dt {
  font-weight: 600;
  margin-top: 0.75em;
  margin-bottom: 0.25em;
  color: var(--text-color);
}

dd {
  margin-left: 1.5em;
  margin-bottom: 0.5em;
  opacity: 0.9;
}

ul {
  margin-top: 0.75em;
  padding-left: 1.25em;
}

li {
  margin-bottom: 1.5em;
}

li > dl {
  margin-top: 0.5em;
}

li > dl dt {
  margin-top: 0.5em;
}

header {
  margin-bottom: 1em;
}

footer {
  scroll-margin-top: 5em;
}

nav {
  display: flex;
  gap: 1.5em;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  padding: 1.2em 1em;
  margin: 0 -20px 1.5em;
  border-bottom: 1px solid var(--heading-border-color);
  position: sticky;
  top: 0;
  background-color: var(--bg-color);
  z-index: 100;
  backdrop-filter: blur(10px);
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.05);
}

nav a {
  font-size: 1em;
  font-weight: 600;
  opacity: 0.85;
  transition: opacity 0.2s ease, color 0.2s ease;
  letter-spacing: 0.01em;
}

nav a:hover {
  opacity: 1;
  text-decoration: none;
  color: var(--link-color);
}

.scroll-to-top {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  padding: 0;
  margin-left: auto;
  background-color: var(--skill-bg-color);
  border: 1px solid var(--skill-border-color);
  border-radius: 50%;
  color: var(--text-color);
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: scale(0.8);
  transition: opacity 0.3s ease, visibility 0.3s ease, transform 0.3s ease, background-color 0.2s ease;
}

.scroll-to-top:hover {
  background-color: var(--link-color);
  color: #ffffff;
  transform: scale(0.9);
}

.scroll-to-top.visible {
  opacity: 1;
  visibility: visible;
  transform: scale(1);
}

.scroll-to-top svg {
  display: block;
}

.logo {
  width: 300px;
  aspect-ratio: 136/45;
  display: block;
  background-image: var(--logo);
  background-size: contain;
  background-position: top left;
  background-repeat: no-repeat;
  transition: background-image 0.3s ease;
}

ul.tags {
  list-style-type: none;
  padding: 0;
  margin-block-start: 0.5rem;
  margin-block-end: 0.5rem;
  display: flex;
  flex-wrap: wrap;
  justify-content: flex-start;
}

ul.tags li {
  display: inline-block;
  margin: 5px 5px 5px 0;
  padding: 5px 10px;
  background: var(--skill-bg-color);
  border: 1px solid var(--skill-border-color);
  border-radius: 3px;
  font-size: 12px;
}

.contact {
  margin-top: 20px;
  border-top: 1px solid var(--heading-border-color);
  padding-top: 20px;
}

@media (max-width: 600px) {
  body {
    padding: 10px;
  }

  h1 {
    font-size: 1.8em;
  }

  h2 {
    font-size: 1.3em;
  }

  h3 {
    font-size: 1.1em;
  }

  nav {
    margin: 0 -10px 1.5em;
    padding: 1em 0.75em;
    gap: 1.2em;
  }

  nav a {
    font-size: 0.95em;
  }

  .scroll-to-top {
    width: 32px;
    height: 32px;
  }

  .scroll-to-top svg {
    width: 18px;
    height: 18px;
  }
}

/* Tech Stack Icons */
.tech-icons-main {
  text-align: center;
  margin: 1.5em 0;
}

.tech-icons-main img {
  max-width: 100%;
  height: auto;
}

.tech-icons-all {
  margin: 2em 0;
  padding: 2em 0 1em;
  border-top: 1px solid var(--heading-border-color);
  opacity: 0.6;
  transition: opacity 0.3s ease;
  overflow: hidden;
}

.tech-icons-all:hover {
  opacity: 1;
}

.tech-icons-all:hover .tech-icons-track {
  animation-play-state: paused;
}

.tech-icons-scroll {
  width: 100%;
  overflow: hidden;
  position: relative;
  -webkit-mask-image: linear-gradient(to right, transparent, black 50px, black calc(100% - 50px), transparent);
  mask-image: linear-gradient(to right, transparent, black 50px, black calc(100% - 50px), transparent);
}

.tech-icons-track {
  display: flex;
  gap: 8px;
  width: fit-content;
  animation: scroll-left 30s linear infinite;
}

.tech-icons-track img {
  height: 48px;
  width: auto;
  display: block;
  flex-shrink: 0;
}

@keyframes scroll-left {
  0% {
    transform: translateX(0);
  }
  100% {
    transform: translateX(-50%);
  }
}