box-sizing: border-box;
}

body {
  font-family: sans-serif;
  margin: 0;
  padding: 0;
}

header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  background-color: #ffffff;
  box-shadow: 0px 0px 10px rgba(0, 0, 0, 0.1);
  z-index: 999;
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 20px;
}

.menu-btn {
  display: none;
  flex-direction: column;
  cursor: pointer;
}

.menu-btn span {
  height: 3px;
  width: 25px;
  background-color: #333333;
  margin-bottom: 5px;
  border-radius: 5px;
}

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

nav li {
  margin-left: 20px;
}

nav a {
  text-decoration: none;
  color: #333333;
  font-weight: bold;
}

main {
  margin-top: 80px;
  padding: 40px;
}

section {
  margin-bottom: 40px;
}

body {
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  line-height: 1.6;
  margin: 0;
  padding: 0;
  color: #333;
  background-color: #f5f5f5;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 15px;
}

section {
  padding: 2rem 0;
}

h1, h2, h3, h4 {
  margin-bottom: 1rem;
}

h1, h2, h3 {
  font-weight: 700;
}

h4 {
  font-weight: 400;
}

h1 {
  font-size: 2.3em;
  position: relative;
  padding: 1.5rem 2rem;
  border: 4px solid #000;
  background-color: #efefef;
  border-radius: 8px;
  box-shadow: 2px 2px 4px rgba(0, 0, 0, 0.2);
}

h1:before,
h1:after {
  position: absolute;
  left: 0;
  width: 100%;
  content: '';
  border-top: 4px dotted #000;
}

h1:before {
  top: 6px;
}

h1:after {
  bottom: 6px;
}

h2 {
  padding: 1rem 2rem;
  border: 3px solid #000;
  background-color: #fff;
  border-radius: 4px;
  box-shadow: 1px 1px 3px rgba(0, 0, 0, 0.1);
}

h3 {
  padding: 1rem 2rem;
  background: #f4f4f4;
  border-radius: 4px;
  box-shadow: 1px 1px 2px rgba(0, 0, 0, 0.1);
}

h4 {
position: relative;
display: inline-block;
padding: 0 65px;
text-align: center;
color: #555;
background-color: #f9f9f9;
border-radius: 4px;
}

h4:before,
h4:after {
position: absolute;
top: calc(50% - 3px);
width: 50px;
height: 6px;
content: '';
border-top: solid 2px #000;
border-bottom: solid 2px #000;
}

h4:before {
left: 0;
}

h4:after {
right: 0;
}

blockquote {
background-color: #f9f9f9;
border-left: 4px solid #ccc;
margin: 1.5rem 1;
padding: 1.0rem 1.0rem 1.0rem 1.0rem;
font-style: italic;
line-height: 1.2;
position: relative;
}

/* Link styles */
a:link, a:visited {
color: #1264A3;
text-decoration: underline;
}

a:hover {
color: #f39700;
text-decoration: none;
}

@media screen and (max-width: 768px) {
header {
flex-direction: column;
align-items: flex-start;
}

.menu-btn {
display: flex;
}

nav {
display: none;
width: 100%;
}

nav.active {
display: block;
}

nav ul {
flex-direction: column;
align-items: center;
}

nav li {
margin: 10px 0;
}
}


#profile {
margin-top: -25px;
padding-top: 25px;
}


#books {
margin-top: -25px;
padding-top: 25px;
}


#papers {
margin-top: -25px;
padding-top: 25px;
}


#presentations {
margin-top: -25px;
padding-top: 25px;
}


#others {
margin-top: -25px;
padding-top: 25px;
}


#lectures {
margin-top: -25px;
padding-top: 25px;
}


#links {
margin-top: -25px;
padding-top: 25px;
}