/* Set up */
* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

:root {
  --ff-primary: 'Inter', sans-serif;
  --ff-sec: charter, Georgia, Cambria, 'Times New Roman', Times, serif;

  --fw-reg: 400;
  --fw-bold: 700;

  --fs-h1: 2.5rem;
  --fs-h2: 2.5rem;
  --fs-h3: 1.6rem;
  --fs-body: 1.4rem;

  --clr-light: #f5f5f5;
  --clr-dark: #1a1c1e;
  --clr-dark-2: #2d2f34;
  --clr-accent: #68d000;
  --clr-shadow: #00000044;

  --foreground: var(--clr-dark);
  --background: var(--clr-light);

  --line-height: 1.4;
  --line-height-2: 1;
}

.darkmode {
  --clr-dark: #1a1c1e;
  --clr-light: #f5f5f5;
  --clr-accent: #68d000;
  --clr-shadow: #68d00092;

  --foreground: var(--clr-light);
  --background: var(--clr-dark);
}

h3 {
  margin-top: 3em;
  font-family: var(--ff-primary);
  font-weight: var(--fw-bold);
}

p {
  letter-spacing: 0.003em;
}

a:hover,
.fake-nav a:hover {
  color: var(--clr-accent);
}
a {
  color: var(--foreground);
}

body {
  margin: 0;
  background-color: var(--background);
  color: var(--foreground);
  font-family: var(--ff-sec);
  font-size: var(--fs-body);
  font-weight: var(--fw-reg);
  line-height: var(--line-height-2);
  min-height: 100vh;
}

/* hero style */

.hero {
  background: linear-gradient(to top, #000000e3, rgba(91, 66, 66, 0.23)),
    url(./images/hero.jpg) no-repeat center center;
  background-size: cover;
  height: 100vh;
  display: flex;
  justify-content: flex-start;
  align-items: flex-end;
  font-size: var(--fs-h1);
  font-family: 'Montserrat', sans-serif;
  text-transform: uppercase;
  color: var(--clr-light);
  padding: 2em;
  box-shadow: 0 0.5rem 1rem var(--clr-shadow);
}

.fake-nav {
  font-size: calc(var(--fs-h3) + 0.2rem);
  font-family: 'Great Vibes', cursive;
  margin-bottom: 0;
  display: flex;
  align-items: center;
  justify-content: space-around;
  height: 3em;
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  color: var(--foreground);
  background-color: var(--background);
  box-shadow: 0 0.5rem 1rem var(--clr-shadow);
  z-index: 100;
  opacity: 1;
  transition: opacity 100ms ease-in;
}

.fake-nav a {
  color: var(--foreground);
  text-decoration: none;
}

.disappear {
  opacity: 0;
}

/* body styling */
.research {
  display: flex;
  flex-direction: column;
  justify-content: center;
  height: auto;
  padding: 7em;
  font-size: var(--fs-body);
  line-height: var(--line-height);
}

.image {
  display: flex;
  justify-content: center;
  margin-bottom: 3em;
  width: 100%;
}

.image img {
  width: 80%;
}

footer {
  width: 100%;
  height: 3em;
  background-color: var(--foreground);
  display: flex;
  justify-content: space-between;
  color: var(--background);
  font-family: var(--ff-primary);
}

footer div {
  width: 30%;
}

footer ul {
  list-style: none;
  display: flex;
  justify-content: space-around;
  align-items: center;
  width: 40%;
  padding: 0;
  font-size: var(--fs-body);
}

div.copyright {
  display: flex;
  justify-content: flex-start;
  align-items: center;
  padding-left: 2em;
  font-size: var(--fs-body);
}

footer a {
  text-decoration: none;
  color: var(--background);
  position: relative;
}

footer a::after {
  content: '';
  width: 100%;
  height: 2px;
  background-color: var(--clr-accent);
  position: absolute;
  bottom: -0.2rem;
  left: 0;
  transform: scaleX(0);
  transition: transform 200ms ease-in;
}

footer a:hover::after {
  transform: scaleX(1);
}

.fade-in {
  transform: translateY(10vh);
  transition: opacity 400ms ease-in, transform 400ms ease-in;
  opacity: 0;
}

.fade-in.appear {
  transform: translateY(0);
  opacity: 1;
}

body {
  -ms-overflow-style: none;
  scrollbar-width: none;
  overflow-y: scroll;
}

body::-webkit-scrollbar {
  display: none;
}
.progress-container {
  position: fixed;
  width: 100%;
  height: 0.3em;
  z-index: 1000;
}

.progress-bar {
  width: 0;
  height: 100%;
  background-color: var(--clr-accent);
}

.btn {
  width: 2em;
  height: 2em;
  display: flex;
  justify-content: center;
  align-items: center;
  border-radius: 50%;
  background-color: var(--clr-accent);
  position: fixed;
  bottom: 3em;
  right: 3em;
  box-shadow: 0 5px 20px var(--clr-shadow);
  transition: opacity 100ms ease-in;
  z-index: 10;
}

.fa-arrow-up-long,
.dark-icon {
  color: var(--foreground);
  font-size: var(--fs-body);
}

.dark-mode-toggle {
  color: var(--foreground);
  border: 0.1em solid var(--foreground);
  display: flex;
  justify-content: center;
  align-items: center;
  background: transparent;
  cursor: pointer;
  border-radius: 0.3em;
  width: 2.5em;
  height: 2.5em;
}

@media screen and (max-width: 970px) {
  :root {
    --fs-h1: 2rem;
    --fs-h3: 1.5rem;
    --fs-body: 1.3rem;
  }
}
@media screen and (max-width: 780px) {
  :root {
    --fs-h1: 1.6rem;
    --fs-h3: 1.4rem;
    --fs-body: 1.2rem;
  }
  .research {
    padding: 4em;
  }
  .copyright {
    padding-left: 1.5em;
    font-size: 1rem;
  }
  .dark-mode-toggle {
    width: 2em;
    height: 2em;
  }
}
@media screen and (max-width: 550px) {
  :root {
    --fs-h1: 1.4rem;
    --line-height-2: 1.2;
    --fs-h3: 1.3rem;
    --fs-body: 1.1rem;
  }
  .research {
    padding: 2em;
  }
  .copyright {
    padding-left: 1em;
  }
}
@media screen and (max-width: 480px) {
  :root {
    --fs-h1: 1.2rem;
    --line-height-2: 1.2;
    --fs-h3: 1.2rem;
    --fs-body: 0.9rem;
  }
  .research {
    padding: 1em;
  }
  .copyright {
    padding-left: 0.5em;
  }
}
@media screen and (max-width: 370px) {
  :root {
    --fs-h1: 1rem;
    --line-height-2: 1.3;
    --fs-h3: 1.1rem;
    --fs-body: 0.8rem;
  }
}
@media screen and (max-width: 310px) {
  :root {
    --fs-h1: 0.8rem;
    --line-height-2: 1.4;
    --fs-h3: 0.8rem;
    --fs-body: 0.7rem;
  }
}
@media screen and (max-width: 260px) {
  :root {
    --fs-h1: 0.6rem;
    --line-height-2: 1.5;
    --fs-h3: 0.7rem;
    --fs-body: 0.6rem;
  }
}