:root {
    --primary-bg: #2c2f33;
    --secondary-bg: #23272a;
    --tertiary-bg: #3a3e42;
    --font-color: #ffffff;
    --primary-accent: #7289da;
    --secondary-accent: #99aab5;
    --border-color: #4a4e53;
    --success-color: #43b581;
    --error-color: #f04747;
    --shadow-color: rgba(0,0,0,0.2);
}

body[data-theme="light"] {
    --primary-bg: #ffffff;
    --secondary-bg: #f2f3f5;
    --tertiary-bg: #e3e5e8;
    --font-color: #2e3338;
    --primary-accent: #5865f2;
    --secondary-accent: #4f5660;
    --border-color: #dcdfe4;
    --shadow-color: rgba(0,0,0,0.1);
}

body {
    font-family: "Microsoft YaHei", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: var(--primary-bg);
    color: var(--font-color);
    margin: 0;
    padding: 0; /* Adjusted for sticky footer */
    box-sizing: border-box;
    transition: background-color 0.3s, color 0.3s;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

.container {
    max-width: 1100px;
    margin: 0 auto;
    padding: 20px; /* Adjusted for sticky footer */
    display: flex;
    flex-direction: column;
    gap: 20px;
    flex-grow: 1; /* Allow container to grow */
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    text-align: center;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 15px;
}

header .title {
    flex-grow: 1;
    text-align: center;
    /* margin-left: 100px; */ /* Offset for the theme switcher */
}

.header-controls {
    display: flex;
    align-items: center;
    gap: 20px;
    position: absolute;
    right: 20px;
    top: 20px;
}

header h1 {
    margin: 0;
    color: var(--primary-accent);
}

nav {
    display: flex;
    justify-content: center;
    gap: 15px; /* Add gap between nav buttons */
}

.nav-btn {
    background-color: var(--secondary-accent);
    color: var(--primary-bg);
    border: none;
    padding: 10px 20px;
    border-radius: 5px;
    cursor: pointer;
    font-size: 1em;
    transition: background-color 0.3s;
}

.nav-btn:hover {
    opacity: 0.9;
}

main {
    display: grid;
    grid-template-columns: 1fr 2fr;
    gap: 20px;
}

.converter-panel, .explanation-panel, .modal-content {
    background-color: var(--secondary-bg);
    padding: 20px;
    border-radius: 8px;
    box-shadow: 0 2px 10px var(--shadow-color);
    transition: background-color 0.3s;
}

.controls {
    display: flex;
    flex-direction: column;
    gap: 15px;
}

.form-group {
    display: flex;
    align-items: center;
    gap: 10px;
}

label {
    font-weight: bold;
    color: var(--secondary-accent);
}

input[type="text"], select {
    width: 100%;
    padding: 8px;
    background-color: var(--tertiary-bg);
    border: 1px solid var(--border-color);
    color: var(--font-color);
    border-radius: 4px;
    transition: background-color 0.3s, color 0.3s, border-color 0.3s;
}

#integer-bases {
    display: flex;
}

button {
    padding: 10px 15px;
    border: none;
    border-radius: 5px;
    background-color: var(--primary-accent);
    color: #ffffff;
    font-size: 1.1em;
    cursor: pointer;
    transition: background-color 0.3s;
}

button:hover {
    opacity: 0.9;
}

.explanation-content {
    background-color: var(--tertiary-bg);
    padding: 15px;
    border-radius: 5px;
    min-height: 200px;
    white-space: pre-wrap;
    font-family: "Microsoft YaHei", "Courier New", Courier, monospace;
    line-height: 1.1;
    transition: background-color 0.3s;
}

.explanation-content .step {
    margin-bottom: 15px;
    padding-bottom: 10px;
    border-bottom: 1px dashed var(--border-color);
}

.explanation-content .step:last-child {
    border-bottom: none;
}

.explanation-content h4 {
    color: var(--primary-accent);
    margin-top: 0;
}

.explanation-content .final-result {
    margin-top: 20px;
    padding: 15px;
    background-color: var(--primary-bg);
    border: 1px solid var(--success-color);
    border-radius: 5px;
    font-weight: bold;
}

.explanation-content .binary-groups span {
    margin: 0 2px;
    padding: 2px;
    border-radius: 3px;
}

/* Modal styles */
.modal {
    display: none; 
    position: fixed; 
    z-index: 1; 
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    overflow: auto; 
    background-color: rgba(0,0,0,0.6);
}

.modal-content {
    margin: 10% auto;
    padding: 30px;
    border: 1px solid var(--border-color);
    width: 60%;
    position: relative;
}

.close-btn {
    color: var(--secondary-accent);
    position: absolute;
    top: 10px;
    right: 20px;
    font-size: 28px;
    font-weight: bold;
    cursor: pointer;
}

.close-btn:hover, .close-btn:focus {
    color: var(--font-color);
}

#concepts-content h3 {
    color: var(--primary-accent);
}

#concepts-content ul {
    list-style-type: none;
    padding-left: 0;
}

#concepts-content li {
    background-color: var(--tertiary-bg);
    margin-bottom: 10px;
    padding: 10px;
    border-radius: 4px;
}

#concepts-content strong {
    color: var(--primary-accent);
}

/* Theme Switcher */
.theme-switcher {
    display: flex;
    align-items: center;
    gap: 10px;
}

.theme-switcher .switch {
    position: relative;
    display: inline-block;
    width: 50px;
    height: 24px;
}

.theme-switcher .switch input { 
    opacity: 0;
    width: 0;
    height: 0;
}

.theme-switcher .slider {
    position: absolute;
    cursor: pointer;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: var(--tertiary-bg);
    transition: .4s;
    border-radius: 24px;
}

.theme-switcher .slider:before {
    position: absolute;
    content: "";
    height: 16px;
    width: 16px;
    left: 4px;
    bottom: 4px;
    background-color: white;
    transition: .4s;
    border-radius: 50%;
}

.theme-switcher input:checked + .slider {
    background-color: var(--primary-accent);
}

.theme-switcher input:checked + .slider:before {
    transform: translateX(26px);
}

/* Hide scrollbar for Chrome, Safari and Opera */
body::-webkit-scrollbar {
    display: none;
}

/* Collapsible section styles */
.expand-btn {
    display: block;
    text-align: right;
    font-size: 0.9em;
    color: var(--secondary-accent);
    cursor: pointer;
    text-decoration: underline;
    margin-top: 5px;
}

.expand-btn:hover {
    color: var(--primary-accent);
}

.collapsible-container p {
    display: none;
    margin: 8px 0;
}

/* Show first 3 by default */
.collapsible-container p:nth-child(-n+3) {
    display: block;
}

/* Show all when expanded */
.collapsible-container.expanded p {
    display: block;
}

/* Ellipsis logic */
.collapsible-container::after {
    content: '...';
    display: block;
    text-align: center;
    margin-top: 5px;
}

.collapsible-container.expanded::after {
    display: none;
}

footer {
    text-align: center;
    padding: 20px 0;
    margin-top: 20px;
    color: var(--secondary-accent);
}

footer a {
    color: var(--primary-accent);
    text-decoration: none;
}

footer a:hover {
    text-decoration: none;
}

/* Responsive Design for Mobile */
@media (max-width: 768px) {
    main {
        grid-template-columns: 1fr; /* Stack the panels vertically */
    }

    header {
        flex-direction: column; /* Stack title and theme switcher */
        gap: 15px;
        position: relative;
        padding-bottom: 70px; /* Add padding to avoid overlap */
    }

    .header-controls {
        position: static;
        flex-direction: column;
    }

    header .title {
        margin-left: 0; /* Remove the offset on mobile */
    }

    .modal-content {
        width: 90%; /* Make modal wider on small screens */
        margin: 20% auto;
    }
}