:root {
    /* Burger menu variables */
    --burger-bg: var(--button-bg);
    --burger-color: rgb(25, 25, 25);
    --burger-icons-color: var(--burger-color);
    --burger-diameter: 2.125em;        /* Size of the circular button */
    --burger-line-width: 1.125em;
    --burger-line-height: 0.125em;
    --burger-offset: 0.625em;         /* Distance of lines from top/bottom edges */
    
    /* Navigation Panel */
    --nav-bg: rgb(230, 230, 230);
    --nav-text-color: rgba(25, 25, 25, 1);
    --nav-border-radius: 0.375em;
    --nav-button-hover-bg: rgb(100, 149, 237);
    --nav-button-hover-text-color: rgb(255, 255, 255);
}

/* Popup burger menu */
.popup {
    position: fixed;
    top: 10px;
    left: 10px;
    display: inline-block;
    text-rendering: optimizeLegibility;
    width: 5.5%;
    z-index: 1000;
    stroke: var(--burger-icons-color);
    user-select: none;
}
.popup input {
    display: none;
}
.burger {
    display: flex;
    align-items: center;
    justify-content: center;
    width: var(--burger-diameter);
    height: var(--burger-diameter);
    background: var(--burger-bg);
    border: none;
    border-radius: 50%;
    cursor: pointer;
    position: relative;
    transition: transform 0.1s ease-in-out;
}
.burger span {
    position: absolute;
    height: var(--burger-line-height);
    width: var(--burger-line-width);
    background: var(--burger-color);
    border-radius: 0.1875em;
    transition: transform 0.3s;
}
.burger span:nth-child(1) {
    top: var(--burger-offset);
}
.burger span:nth-child(2) {
    bottom: var(--burger-offset);
}
.burger span:nth-child(3) {
    top: 50%;
    transform: translateY(-50%);
}
.burger:hover {
    transform: scale(1.1);
}
.burger:active {
    transform: scale(0.95);
}
.popup input:checked + .burger span:nth-child(1) {
    top: 50%;
    transform: translateY(-50%) rotate(45deg);
}
.popup input:checked + .burger span:nth-child(2) {
    bottom: 50%;
    transform: translateY(50%) rotate(-45deg);
}
.popup input:checked + .burger span:nth-child(3) {
    transform: translateX(calc(-1 * var(--burger-diameter) - var(--burger-line-width)));
}
.popup-window {
    position: absolute;
    top: calc(var(--burger-diameter) + 0.25em);
    left: 0;
    background: var(--nav-bg);
    color: var(--nav-text-color);
    border-radius: var(--nav-border-radius);
    box-shadow: 0 1px 5px rgba(0, 0, 0, 0.2);
    border: 1px solid var(--h3-color);
    padding: 0.625em 0.25em;
    visibility: hidden;
    opacity: 0;
    transform: scale(0.8);
    transition: all 0.1s ease-in-out;
}
.popup input:checked ~ .popup-window {
    visibility: visible;
    opacity: 1;
    transform: scale(1);
}
.popup-window legend {
    font-size: 0.625em;
    color: rgb(119, 119, 119);
    text-transform: uppercase;
    padding: 0.25em 3.25rem;
}
.popup-window ul {
    list-style: none;
    margin: 0;
    padding: 0;
    font-size: 0.7em;
}
.popup-window ul button {
    background: none;
    border: none;
    display: flex;
    align-items: center;
    padding: 0.375em 1rem;
    border-radius: 0.375em;
    cursor: pointer;
    gap: 0.875em;
    color: var(--burger-color);
    font-size: 10px;
}
.popup-window ul button:hover, .popup-window ul button:focus-visible {
    background: var(--nav-button-hover-bg);
    color: var(--nav-button-hover-text-color);
}
.popup-window hr {
    border: none;
    border-bottom: 0.0625em solid rgb(204, 204, 204);
    margin: 0.3125em 0;
}