theme.css

body {
    font-family: 'Open Sans', sans-serif;
    color: #333;
    background-color: #fff;
    line-height: 1.6;
}

p {
    margin: 0px;
}

.normal_text {
    color: #fff;
}

.hamburger-menu span {
    background-color: #333;
}

a {
    color: #0067cc;
    text-decoration: none;
}

a:hover {
    text-decoration: underline;
}

.content {
    width: 80%;
    margin: auto;
    overflow: hidden;
}

header {
    background: #f4f4f4;
    color: #333;
}


header a {
    text-decoration: none;
    margin: 0 15px;
    text-transform: uppercase;
}

@media (max-width: 700px) {
    .content {
        width: 95%;
    }
}


footer {
    background: #f4f4f4;
    color: #333;
    text-align: center;
    padding: 20px 0;
    width: 100%;
}

@media (prefers-color-scheme: dark) {
    body {
        color: #E0E0E0;
        background-color: #212121;
    }

    header {
        background-color: black;
    }

    a, a:visited {
        color: #BBDEFB;
    }

    header, footer {
        background: black;
        color: white;
    }
    .hamburger-menu span {
        background-color: white;
    }
}
header {
    height: 100%;
    width: 200px;
    position: fixed;
    top: 0;
    left: 0;
    overflow-x: hidden;
    padding-top: 20px;
    padding: 1em 0;
    display: flow-root list-item;
    border-right: 1px solid #ddd;
    z-index: 1000;
    box-shadow: 0px 2px 4px rgba(0, 0, 0, 0.2);
}
header a {
    text-decoration: none;
    font-weight: bold;
    margin-left: 15px;
    text-align: left;
    line-height: 2.6;
    white-space: nowrap;
}
.content {
    padding: 20px;
    margin-left: 210px;
    overflow: hidden;
}
header nav ul {
    list-style: none;
    padding: 0;
    margin: 0;
}
header nav ul li .submenu-toggle {
    display: none;
}
.submenu {
    padding-left: 20px;
    font-size: 80%;
}
@media (max-width: 768px) {
    header {
        padding-left: 10px;
        height: auto;
        width: 100%;
    }
    .content {
        padding: 40px 5px;
        margin-left: 0px;
        width: 100%;
    }
}
header .hamburger-menu {
    display: none;
    cursor: pointer;
    flex-direction: column;
    justify-content: space-around;
    height: 30px;
    width: 30px;
    margin-left: auto;
}

.hamburger-menu span {
    display: block;
    height: 3px;
    width: 100%;
    border-radius: 3px;
}

@media (max-width: 768px) {
    header .hamburger-menu {
        padding: 0px;
        display: flex;
        margin-left: 0px;
    }

    header a {
        display: none;
    }

    header.nav-active a {
        display: block;
        padding: 10px;
        text-align: center;
    }

    header.nav-active {
        flex-direction: column;
    }

    header nav ul {
        display: none;
        flex-direction: column;
    }

    header.nav-active nav ul {
        display: flex;
    }

    header nav ul li .submenu-toggle {
        display: inline-block;
        vertical-align: top;
        margin-left: 5px;
        cursor: pointer;
    }

    header nav ul li ul.submenu {
        display: none;
        position: static;
        flex-direction: column;
    }

    header nav ul li.submenu-active ul.submenu {
        display: block;
    }

    header nav ul li {
        display: flex;
        align-items: center;
    }
}

header, header a {
      color: #ffffff;
}
header {
      background-color: #1976d2;
}
@media (prefers-color-scheme: dark) {
  body {
        color: #ffffff;
  }
  header, header a {
        color: #ffffff;
  }
  header {
        background-color: #1565c0;
  }
  a {
        color: #ffffff;
  }
}