index.css

* {
	margin: 0;
	padding: 0;
}

body {
    /* font-family: system-ui, Special Elite, BlinkMacSystemFont, Roboto, arial, sans-serif; */
    font-size: 12px;

}

/* I added a class btn-toggle used to change the theme to dark mode */
.btn-toggle{
    background-color:#4b4a4afb;
    width: 80px;
    font-size: 10px;
    padding-top: 1px;
    font-weight: 900;
    font-family: Raleway;
    color: white;
    border-radius: 10px;
    cursor: pointer;
}
/*Google logo is a background image of a h1 block*/
h1#logo {
    height: 150px;
    width: 272px;
    background: url("images/googlelogo_color_272x92dp.png") top left no-repeat;
    background-size: 100%;
    margin:  0 auto;
}
/*the container for the center contents*/
#mainContainer {
    width: 580px;
    margin: 150px auto 0;
    text-align: center;
    font-family: Special Elite;
    font-size: x-large;
}

.search-bar {
    position: relative;
    margin: 25px 0 25px 0;
}

/*search box I added an ID { "searchBox"  }*/
input[type="text"] {
    outline: none;
    height: 44px;
    border: 1px solid rgba(223, 225, 229);
    font-size: 16px;
    border-radius: 24px;
    box-sizing: border-box;
    width: 44px;
    color: #444;
    background-color: white;
    text-indent: 2.6em;
    box-shadow: 0 1px 6px 0 rgba(32, 33, 36, .28);
    transition: width .5s ease-in-out;
}
/*still refers to search box*/
input[type="text"]:hover {
	width: 584px;
}
/*still refers to search box*/
input[type="text"]:focus {
    width: 584px;
    outline: none;
}

/*Search box icon "Search"*/

.search-bar-icons--search {
    width: 20px;
    position: absolute;
    left: 15px;
    top: 12px;
    opacity: 0;
    transition: 1s;
}

/* Search box icon "MIC" */

.search-bar-icons--mic {
    width: 25px;
    position: absolute;
    right: 15px;
    top: 10px;
    opacity: 0;
    transition: opacity 1s;
}

/* Icons animation */

.icons-animated {
    display: block;
    opacity: 1;
    transition: opacity 2s;
}

/*refers to google search button*/

input[type="submit"] {
    /* background-color: rgba(242, 242, 242); */
    background-color: #444;
    color: #fff;
    padding: 10px 15px;
    font-size: 13px;
    border: none;
     /* color: rgba(85, 89, 93);  */
    margin: 4px;
    border-radius: 4px;
    cursor: pointer;
    transition: all .5s ease-in-out;
}

input[type="submit"]:hover {
    /* background-color: #444;*/
    color: #d7e916; 
    transform: scale(1.1);
}

input[type="submit"] small {
    display: block;
    margin: 20px 0 0;
    font-size: 12px
}

nav#header {
    padding: 20px;
    display: flex;
    justify-content: space-between;
}

nav ul {
    display: flex;
    align-items: center;
    justify-content: center;
}

.app-icon {
    width: 25px;
    margin-right: 20px;
    margin-left: 10px;
    transition: 0.15s;
    filter: brightness(100%);
}
/*this changes the opacity of icon with transition of 0.15s */
.app-icon:hover {
/* this gives the rotation animation to app-icon when we hover it */
    transition: transform 0.5s ease-in-out;
    transform: rotateZ(180deg);
     filter: brightness(100%); 
    box-shadow:0.2px 0.2px 8px rgb(80, 79, 79);  
    cursor:pointer;
}

#appPocket {
    display: none;
    position: absolute;
    overflow: hidden;
    top: 0px;
    right: 0px;
    width: 330px;
    height: 601px;
    margin-top: 57px;
    margin-right: 4px;
    border: black solid 1px;
}

nav ul li{
    display: inline-block;
}
/* this changes the appearance of link when visited and not visited */
nav#header ul li a:link,
nav#header ul li a:visited {
    color: #40675f;   
    text-decoration: none;
    padding: 10px;
    font-family: Raleway;
    font-size: 15px;
    font-weight: 600;
}
/* sign-in button*/
nav#header ul li #signIn {
    background-color: rgba(62, 129, 251, 1.0);
    padding: 5px 10px;
    border-radius: 2px;
    color: white;
}
/* This is the sign in button change */
#signIn:hover{
    filter: brightness(150%);
    background-color: rgba(69, 117, 199, 0.836);
    box-shadow: 0 0 5px 1px #4884eb;
}


/* underlines links on pointer hover */
nav#header ul li a:hover {
    text-decoration: none;
    color: #d7e916;
}

footer {
    position: fixed;
    bottom: -28px;
    background-color: rgb(41, 39, 39);
    padding: 12px 0;
    width: 100%;
    transition: transform 0.2s ease-in-out;
    cursor: pointer;
}

footer:hover, footer.slide {
    transform: translateY(-28px);
}

footer nav {
    padding: 0 12px;
}

footer nav ul li {
    padding: 0 12px;
}

footer nav ul li a{
    color: rgba(85, 89, 93);
    text-decoration: none;
}

footer nav ul li a:hover {
    text-decoration: underline;
}

footer nav ul {
    float: left;
}

footer nav ul#rightLinks {
    float: right;
}

.linksTo {
    padding: 50px;
    font-size: 15px;
    text-decoration: none;
    color: #40675f;
    font-family: Special Elite;
}
/* added this code which for dark-theme toggling */
body{
    background-color: #fff;
    color: #222;
}
body.dark-theme {
    background-color: #242323fb;
    color: #eee;
}
@media(prefers-color-scheme: dark){
    /* This sets default theme as Dark */
    body{
        background-color:#242323fb;
        color:#eee;
    }
    body.light-theme{
        background-color: #fff;
        color: #222;
    }
}