* {                     /*reset the default styles of HTML elements*/
    padding: 0;
    margin: 0;
    text-decoration: none;
    list-style: none;
    box-sizing: border-box;
}

body {
    font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
    background-color: #F5F7F9;;
}

/* styling nav bar */
nav{
    position: fixed;
    top: 0;
    z-index: 2;
    font-family: 'Poppins', sans-serif;
    display: flex;
    height: 95px;
    width: 100%;
    background-color: transparent;
    align-items: center;
    justify-content: space-between;
    padding: 0 0 0 50px;
    flex-wrap: wrap;
    transition: background-color 0.2s ease-in-out;
}

nav.scrolled {
    background-color: #253177;

}  

.logo.scrolled {
    color: #fff;
}

nav ul li a.scrolled  {
    color: #f2f2f2;
}   

nav .tutor.scrolled {
    color: #fff;
    background-color: #374EFF;
    font-weight: 700;
    font-size: 14px;
    padding: 15px 40px;
    border-radius: 4px;
    box-shadow: 3px 3px 7px 2px rgb(109 121 255 / 30%);
}


  nav .logo{
    color: rgb(99, 118, 161);
    transition: color 0.2s ease-in-out;
    font-size: 35px;
    font-weight: 600;   

  }
  nav ul{
    display: flex;
    flex-wrap: wrap;
    list-style: none;
    position: absolute;
    right: 0;
    top: 30%;
  }

  nav ul li{
    margin: 0 16px;
    position: relative;
  }
  
  .search-form input[type="text"] {   /*attribute selector, using attribute to style, attribute = "value" */
    padding: 5px;                   /*为指定的attribute加上css*/
    border-radius: 5px;             /*exp: input[type="text"] targets all <input> elements that have a type attribute with a value of text.*/
    width: 200px;
    height: 33px;
    outline: none;  /* Remove the default blue outline */
    border: none;
}


.search-form {
    border: 0.5px solid lightgray;
    background-color: white;
    border-radius: 7px;
}
  
.search-form button[type="submit"] {
    background-color: transparent;
    color: gray;    
    border: none;
    padding: 5px 10px;
    cursor: pointer;
    transition: background-color 0.3s ease;
}
  nav ul li a{
    color: rgb(99, 118, 161);
    font-size: 18px;
    font-weight: 500;
  }


  nav .menu-btn i{
    color: #fff;   
    font-size: 22px;
    cursor: pointer;
    display: none;
  }
  
  input[type="checkbox"]{
    display: none;
  }

.layer {
    width: 70px;
    height: 70px;
    transition: 0.3s;
    margin-left: 10px;
}

.layer i{
    position: absolute;
    top: 0;
    left: 0;
    width: 40%;
    height: 45%;
    border: 1px solid var(--c);
    border-radius: 6px;
    transition: 0.3s;
    display: flex;
    justify-content: center;
    align-items: center;
}

nav .text { 
    position: absolute;
    bottom: 0;
    opacity: 0;
    width: 100%;
    left: -30%;
    text-align: center;
    color: var(--c);        /* call var() to a customization --c */
    transition: 0.3s;
}

nav ul a:hover .text {
    opacity: 1;
}


nav li a:hover .layer {
    transform: rotate(-35deg) skew(20deg);
}

nav li a:hover .layer i:nth-child(1) {
    opacity: 0.2;
    transform: translate(0,0);
}

nav li a:hover .layer i:nth-child(2) {
    opacity: 0.4;
    transform: translate(5px,-5px);
}

nav li a:hover .layer i:nth-child(3) {
    opacity: 0.6;
    transform: translate(10px,-10px);
}

nav li a:hover .layer i:nth-child(4) {
    opacity: 0.8;
    transform: translate(15px,-15px);
}

nav li a:hover .layer i:nth-child(5) {
    opacity: 1.0;
    transform: translate(20px,-20px);
}

/* customize --c */
nav li:nth-child(1) .layer i, li:nth-child(1) .text {
    --c: #12b7f5;
}

nav li:nth-child(2) .layer i, li:nth-child(2) .text {
    --c: #2aae67;
}


nav li:nth-child(3) .layer i, li:nth-child(3) .text {
    --c: #e79115;
}


nav li:nth-child(4) .layer i, li:nth-child(4) .text {
    --c: #2075fd;
    
}


nav li:nth-child(5) .layer i, li:nth-child(5) .text {
    --c: #2d8dc5;
}

nav li:nth-child(8) .layer i, li:nth-child(8) .text {
    --c: rgb(198, 56, 56);
}



/* styling main body */
.intro {
    width: 100%;
    height: 700px;
    position: relative;
}

.intro-pic {
    width: 200px;
    height: 200px;
    border-radius: 50%;
    border: 10px solid lightslategray;
    overflow: hidden;
    position: absolute;
    left: 625px;
    top: 15%;
}

.intro-pic img {
    width: 100%;
    height: 100%;
    object-fit: cover;
}

.intro-content {
    width: 800px;
    height: 200px;
    position: absolute;
    left: 23%;
    top: 50%;
}

.ot-cs {
    display: flex;
    position: absolute;   
    top: 15%;
    left: 4%;
    font-size: 14px;
}

.ot-cs a {
    margin-right: 10px;
}

.ot-cs a:hover {
    text-decoration: underline;
}

.first-row {
    text-align: center;
    position: absolute;
    line-height: 25px;
    left: 10%;
}

.row {
    margin-bottom: 30px;
}

.row a {
    background-color: #374EFF;
    color: white;
    font-weight: 700;
    font-size: 14px;
    padding: 15px 45px;
    border-radius: 4px;
}

.row h1 {
    font-size: 32px;
    color: rgb(46, 47, 109);
}

.row1 p {
    color: rgb(94, 112, 156);
    font-weight: 400;
    font-size: 17px;
}

.row a:hover {
    filter: brightness(1.2);
}

/* styling cards */
.all-cards {
    position: relative;
    width: 100%;
    height: 3300px;
}

.cards {
    position: absolute;
    left: 4%;
}

.card {
    display: flex;
    width: 70%;
    background-color: #fff;
    padding: 3em 2em 2em;
    border-radius: 20px;
    margin-bottom: 30px;
}

.card img {
    border-radius: 50%;
    width: 10%;
    height: 10%;
    margin-right: 30px;
}

.text {
    line-height: 25px;

}

.rows {
    display: flex;
    justify-content: space-between;
    margin-bottom: 20px;
}

.details a {
    border: 1px solid transparent;
    background-color: #374EFF;
    color: white;
    padding: 8px 20px;
    border-radius: 5px;
    font-size: 14px;
    box-shadow: 0 4px 6px rgb(50 50 93 / 11%), 0 1px 3px rgb(0 0 0 / 8%);
}

.details a:hover, .col-text a:hover {
    filter: brightness(0.8);
}

.last small {
    background-color: rgb(243, 243, 243);
    padding: 3px 12px;
    border-radius: 10px;
    margin-right: 5px;
    font-size: 12px;
    color: #374EFF;
}

.method {
    font-size: 13px;
    font-weight: 500;
    margin-bottom: 20px;
}

.desc {
    color: #6376a1;
    font-size: 16px;
    font-weight: 400;
    margin-bottom: 30px;
}

.method span {
    color: #0d8746
}

/* styling col-card */
.col-card {
    position: absolute;
    width: 300px;
    height: 650px;
    right: 4%;
    background-color: #fff;
}

.col-card-pic {
    width: 300px;
    height: 250px;

}

.col-card-pic img {
    width: 100%;
    height: 100%;
    border-top-left-radius: 10px;
    border-top-right-radius: 10px;
}

.col-card-content {
    position: absolute;
    line-height: 25px;
    width: 300px;
    height: 400px;
}

.col-card-content h2 {
    position: absolute;
    top: 3%;
    left: 6%;
    font-size: 22px;
    font-weight: 700;
    margin-bottom: 20px;
}

.col-card .col-card-content p {
    position: absolute;
    left: 6%;
    top: 35%;
    font-size: 13px;
    color: #6376a1;
    margin-bottom: 20px;
}

.col-card-content .col-last {
    position: absolute;
    bottom: 27%;
    left: 6%;
    width: 85%;
    display: flex;
    justify-content: space-between;
}

.col-card-content a {
    border: 1px solid transparent;
    background-color: #374EFF;
    color: white;
    padding: 15px 45px;
    border-radius: 5px;
    font-size: 14px;
    position: absolute;
    bottom: 25px;
    left: 20%;
}

.col-card2 {
    position: absolute;
    width: 300px;
    height: 530px;
    top: 21%;
    right: 4%;
    background-color: #fff;
}

.col-card2 .col-card-pic {
    width: 100px;
    height: 100px;
    margin: 3% auto 0;
    

}

.col-card2 .col-card-pic img {
    width: 100%;
    height: 100%;
}

.col-card2 .col-card-content .text{
    position: absolute;
    left: 6%;
    top: 23%;
    font-size: 13px;
    color: #6376a1;
}

.col-card2 .serious {
    width: 80%;
    position: absolute;
    top: 48%;
    left: 10%;
    background-color: rgb(241, 241, 241);
    padding: 10px;
    line-height: 28px;
    border-radius: 3px;
}

.col-card2 .serious p {
    font-size: 13px;
    color: #6376a1;
}

/* styling contact */
.contact {
    width: 100%;
    height: 350px;
    position: relative;
}

.contact-content {
    position: absolute;
    width: 350px;
    height: 350px;
}

.contact-content a{
    display: flex;
    width: 100%;
    height: 100%;
    border: 1px solid rgb(53, 148, 53);
    background-color: rgb(53, 148, 53);    
    align-items: center;
    justify-content: center;
    color: #F4f9ff;

}

.contact-content a:hover {
    background-color: rgb(208, 159, 69);
    border: 1px solid rgb(208, 159, 69);
    transition-duration: 0.5s;
}

.contact-pic {
    position: absolute;
    left: 40%;
    width: 700px;
    height: 350px;
}

.contact-pic img {
    width: 100%;
    height: 100%;
}

/* styling footer */
.footer-blue {
    position: relative; 
    background-color: lightslategray;
    width: 1074px;
    height: 770px;
    margin: 0 0 0 351px;
}

.gray {
    width: 300px;
    height: 300px;
    position: absolute;
    left: 0;
    top: 0;
    border: 1px solid rgb(225, 224, 224);
    background-color: lightgray;
    display: flex;
    justify-content: center;
    align-items: center;
}

.footer-details {
    width: 700px;
    position: absolute;
    font-size: 14px;
    height: 700px;
    left: 32%;
    color: white;
    top: 7%;
}

.footer-details > p {
    margin-bottom: 40px;
    line-height: 23px;
}

.contact-method {
    margin-bottom: 30px;
    width: 400px;
    display: flex;
    justify-content: space-between;
}

.contact-method a {
    display: inline-block;
    width: 40px;
    height: 40px;
    margin: 0 10px;
    background-color: #fff;
    border-radius: 50%;
    box-shadow: 0 0 6px rgba(0, 0, 0, 0.5);
    transition: all 0.3s ease-in-out;
}

.contact-method a:hover {
    transform: translateY(-5px);
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.5);
}

.contact-method a:nth-child(1) {
    background-color: #3b5998;
}
  
.contact-method a:nth-child(2) {    
    background-color: #0077b5;
}

.contact-method a:nth-child(3) {
    background-color: #1da1f2;
}

.contact-method a:nth-child(4) {
    background-color: #e4405f;
}

.contact-method a i {
    line-height: 40px;
    display: flex;
    justify-content: center;
    text-align: center;

}

.footer-blue table {
    width: 700px;
    height: 400px;
    line-height: 30px;
}

.footer-details a {
    color:  white;
}

.footer-details table a:hover {
    text-decoration: none;
}

.footer-details a:active {
    color: darkblue;
}

.footer-details table a {
    text-decoration: underline;
}


.copyRight {
    position: absolute;
    width: 650px;
    bottom: 20px;
    display: flex;
    justify-content: space-between;

}

.privacy {
    cursor: pointer;
} 

/* Back-page links */
.cta {
    position: fixed;
    z-index: 3;
    top: 88%;
    left: 4%;
    display: flex;
    padding: 10px 15px;
    text-decoration: none;
    font-family: 'Poppins', sans-serif;
    font-size: 15px;
    color: white;
    width: 5%;
    align-items: center;
    text-align: center;
    justify-content: center;
    background: #6225e6;
    transition: 1s;
    box-shadow: 6px 6px 0 black;
    transform: skewX(-15deg);
}

.cta:focus {
    outline: none;
}

.cta:hover {
    transition: 0.5s;
    box-shadow: 10px 10px 0 #fbc638;
    
}

.wrapper span {
    transform: skewX(15deg);
}