timeline.css

/*use the universal selector to set some styles*/
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --white: #fff;
    --light-blue: lightblue;
    --color-blue: blue;
    --color-dark-grey: #222831;
}

/*withe this font size, anywhere we use rem  our styling,  wl be translated to the rem X 10px, normally , 1
1 rem is 16px*/
html {
    font-size: 10px;
}

@import url('https://fonts.googleapis.com/css2?family=Open+Sans:ital,wght@1,500&display=swap');

body {
    font-family: 'Open Sans', sans-serif;
}
  
/* Start Here */
.intro-text {
    background-color: var(--color-dark-grey);
    color: var(--white);
    padding: 2rem 0;
}
  
.container {
    margin: 0 auto;
    padding: 0 20px;
    text-align: center;
}
  
.intro-text h1 {
    font-size: 2.5rem;
}

p {
    font-size: 1.5rem;
    padding-top: 2rem;
    line-height: 1.6;
}

/*Timeline section*/
img {
    width: 100%;
}

.timeline-section {
    width: 100%;
    overflow: hidden;  /* creates block formatting context */
}

.timeline-section ul {
    background: var(--light-blue);
    padding: 5rem 0; /* padding top and bottom 5rem */
}

/*styling the liSt*/
.timeline-section ul li {
    list-style: none;
    position: relative;
    width: 5px; /* set width to 5px then set background to lightblue for that width */
    margin: 0 auto; /* center text */
    padding-top: 5rem; /* separate each list with a padding-top of 5rem = 5 x 10px= 50px */
    background: var(--color-blue);
}

/*use pseudo elements to style*/
/*This section will help us make the node-like structure - The circle*/
.timeline-section ul li::after {
    content: "";/* The content attribute is required for pseudo-elements to render */
    position: absolute;
    left: 50%;
    bottom: 0;
    transform: translateX(-50%);
    width: 3rem;
    height: 3rem;
    border-radius: 50%;
    background: inherit; /* inherits this property from its parent element */
}


/* Content box */
.timeline-section ul li div {
    width: 40rem;
    font-size: 1.2rem;
    position: relative;
    bottom: 0;
    padding: 1.5rem;
    /*glassmorphism effect*/
    background: rgba(255,255,255,.2);
    -webkit-backdrop-filter: blur(5px);
    backdrop-filter: blur(5px);
    box-shadow: 20px 20px 50px rgba(0, 0, 0, 0.5);
    border-radius: 10px;
    border-top: 2px solid rgba(255, 255, 255, 0.5);
    border-left: 2px solid rgba(255, 255, 255, 0.5);
    border-bottom: 2px solid rgba(255, 255, 255, 0.5);
    border-right: 2px solid rgba(255, 255, 255, 0.5);
    border: 1px solid rgba(255,255,255,0.2);
}

/* Triangle */
.timeline-section ul li div::before {
    content: "";
    position: absolute;
    bottom: 7px;
    width: 0;
    height: 0;
    border-style: solid;
}

/*This is to select the divs at odd position so we can separate the divs to the right part*/
.timeline-section ul li:nth-child(odd) div {
    left: 45px;  /* this style pushes the divs at odd number position to the right */
}
  
/*this showcases the triangle*/
.timeline-section ul li:nth-child(odd) div::before {
    left: -15px;
    border-width: 8px 16px 8px 0;
    border-color: transparent var(--light-blue) transparent transparent;
}
 
/*This is to select the divs at even number position so we can separate the divs to the left part*/
.timeline-section ul li:nth-child(even) div {
    left: -439px;
}
  
/*this showcases the triangle*/
.timeline-section ul li:nth-child(even) div::before {
    right: -15px;
    border-width: 8px 0 8px 16px;
    border-color: transparent transparent transparent var(--light-blue); 
}

/*style the time tag*/
time {
    display: block;
    font-size: 1.1rem;
    font-weight: 800;
    margin-bottom: 7px;
}

.timeline-section ul li::after {
    transition: all 0.5s ease-in-out;
}  

 
/*this changes the node content..giving it a background of white and making the border thicker*/
.timeline-section ul li.slide-in::after {
    background: var(--white);
    border: 3px solid var(--light-blue);
}

/* Hide event card initially */
.timeline-section ul li div {
    visibility: hidden;
    opacity: 0;
    transition: all 0.5s ease-in-out;
}
  
.timeline-section ul li:nth-child(odd) div {
    transform: translateX(20rem);
}

.timeline-section ul li:nth-child(even) div {
    transform: translateX(-20rem);
}

/* display the event card */
.timeline-section ul li.slide-in div {
    transform: none;
    visibility: visible;
    opacity: 1;
}

/* Tablet Width */
@media screen and (max-width: 900px) {
    .timeline-section ul li div {
      width: 25rem;
   }

.timeline-section ul li:nth-child(even) div {
      left: -289px;
    }
}

/* Mobile width */
@media screen and (max-width: 600px) {
    .timeline-section ul li {
      margin-left: 2rem;
    }
  
    .timeline-section ul li div {
      width: calc(100vw - 91px);
    }
  
    .timeline-section ul li:nth-child(even) div {
      left: 45px;
    }
  
    .timeline-section ul li:nth-child(even) div::before {
      left: -15px;
      border-width: 8px 16px 8px 0;
      border-color: transparent var(--light-blue) transparent transparent;
    }
}