body {
    background-color: black;
    color: white;
} 

.dark-mode {
    background-color: white;
    color: black;
}

#header {
    background-color: purple;
    border-bottom: 5px solid gray;
    color: white;
    text-align: center;
    margin: 0px -15px;
    margin-top: -10px;
    padding: 1% 0%;
    width: auto;
}

.topnav {
    background-color: black;
    overflow: hidden;
    border-bottom: 5px solid gray;
    margin: 0px -15px;
}

.topnav a {
    float: left;
    color: white;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    font-size: 24px;
    border-right: 1px solid gray;
    font-family: "Black Ops One", system-ui;
    font-weight: 400;
    font-style: normal;
}

.topnav a:hover {
    background-color: purple;
    color: white;
}

.active {
    background-color: purple;
    color: white;
}

.responsive {
    width: 100%;
    height: auto;
}

.tab {
    display: block;
    overflow: hidden;
    background-color: black;
    color: white;
    float: left;
    border: 2px solid gray;
    border-radius: 15px;
    width: 30%;
    height: 100%;
}

body.dark-mode .tab {
  background-color: white;
  color: black;
  }

.tab button {
    display: block;
    background-color: inherit;
    color: inherit;
    padding: 20px 15px;
    width: 100%;
    border: none;
    outline: none;
    text-align: left;
    transition: 0.3s;
    font-size: 24px;
    font-family: "Black Ops One", system-ui;
    font-weight: 400;
    font-style: normal;
}

.tab button:hover {
    background-color: purple;
    color: white;
}

.tab button.active {
    background-color: purple;
    color: white;
}

.tabcontent {
    float: left;
    padding: 0px 10px;
    border: 2px solid gray;
    margin-left: 5px;
    border-radius: 15px;
    width: 69%;
    height: 100%;
}

* {box-sizing: border-box}