:root {
    --color-bg-main: #f7f9fb;
    --color-bg-section: #f0f4fa;
    --color-bg-card: #f8fafc;
    --color-bg-btn: #e3e9f7;
    --color-bg-btn-hover: #d0d8ee;
    --color-text-main: #222;
    --color-text-accent: #4f8cff;
    --color-text-secondary: #2a4d8f;
    --color-border: #b3c6e0;
    --color-tip-bg: #fef9c3;
    --color-tip-border: #fde047;
    --color-tip-text: #b8860b;
    --color-note-bg: #e0f2fe;
    --color-note-text: #217dbb;

    --font-main: 'Segoe UI', Arial, sans-serif;
    --font-size-base: 1rem;
    --font-size-h1: 2.2rem;
    --font-size-h2: 1.4rem;
    --font-size-h3: 1.1rem;
    --font-size-code: 0.98rem;
    --font-weight-bold: 700;
    --font-weight-semi: 600;

    --space-xs: 0.5rem;
    --space-sm: 0.8rem;
    --space-md: 1.2rem;
    --space-lg: 2rem;
    --space-xl: 2.5rem;

    --radius-card: 0.8rem;
    --radius-btn: 0.4rem;

    --shadow-1: 0 0.0625rem 0.25rem #0001;
    --shadow-2: 0 0.0625rem 0.5rem #0001;
    --shadow-3: 0 0.125rem 0.5rem #0002;
    --shadow-4: 0 0.25rem 1rem #4f8cff33;
    --shadow-5: 0 0.25rem 2rem #0002;
}

body {
    font-family: var(--font-main);
    background: var(--color-bg-main);
    color: var(--color-text-main);
    margin: 0;
    padding: 0;
    font-size: var(--font-size-base);
}

.back-nav {
    margin-top: var(--space-lg);
    margin-left: var(--space-lg);
}
.back-btn {
    display: inline-block;
    background: var(--color-bg-btn);
    color: var(--color-text-secondary);
    text-decoration: none;
    padding: var(--space-xs) var(--space-md);
    border-radius: var(--radius-btn);
    font-weight: var(--font-weight-semi);
    transition: background-color 0.2s;
    box-shadow: var(--shadow-1);
}
.back-btn:hover {
    background: var(--color-bg-btn-hover);
}

.appearance-main {
    max-width: 56rem;
    margin: var(--space-xl) auto;
    background: var(--color-bg-card);
    border-radius: var(--radius-card);
    box-shadow: var(--shadow-5);
    padding: var(--space-xl) var(--space-lg) var(--space-lg) var(--space-lg);
}

.appearance-header {
    text-align: center;
    margin-bottom: var(--space-xl);
}
.appearance-header h1 {
    font-size: var(--font-size-h1);
    font-weight: var(--font-weight-bold);
    margin: 0.2rem 0 0.1rem 0;
}
.appearance-header .highlight {
    color: var(--color-text-accent);
}
.subtitle {
    color: var(--color-text-accent);
    font-size: var(--font-size-h3);
    margin-bottom: var(--space-xs);
}

.theory-section {
    background: var(--color-bg-section);
    border-radius: var(--radius-card);
    padding: var(--space-lg) var(--space-lg) var(--space-md) var(--space-lg);
    margin-bottom: var(--space-xl);
    box-shadow: var(--shadow-2);
}
.theory-section h2 {
    margin-top: 0;
    color: var(--color-text-secondary);
}
.theory-list {
    margin: 1rem 0 1rem 1.5rem;
    padding: 0;
    list-style: disc inside;
}
.theory-list li {
    margin-bottom: var(--space-xs);
    font-size: 1.05rem;
}
.syntax-block {
    background: var(--color-bg-main);
    border-left: 0.25rem solid var(--color-text-accent);
    padding: 1rem 1.5rem;
    border-radius: var(--radius-btn);
    margin-bottom: var(--space-md);
}
.tip-block {
    display: flex;
    align-items: center;
    background: var(--color-tip-bg);
    border-left: 0.25rem solid var(--color-tip-border);
    padding: 0.7rem 1.2rem;
    border-radius: var(--radius-btn);
    margin-bottom: var(--space-md);
    font-size: 1.04rem;
    color: var(--color-tip-text);
}
.tip-icon {
    font-size: 1.3rem;
    margin-right: 0.5rem;
}

.examples-section {
    margin-bottom: var(--space-xl);
}
.example-grid {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-md);
    margin-bottom: var(--space-md);
}
.example-card {
    background: var(--color-bg-section);
    border-radius: var(--radius-card);
    box-shadow: var(--shadow-2);
    padding: var(--space-md) var(--space-md) 1.2rem var(--space-md);
    flex: 1 1 15rem;
    min-width: 13rem;
    max-width: 22rem;
    display: flex;
    flex-direction: column;
    align-items: center;
    transition: box-shadow 0.2s, transform 0.2s;
}
.example-card:hover {
    box-shadow: var(--shadow-4);
    transform: translateY(-0.18rem) scale(1.03);
}
.code-block {
    background: var(--color-bg-main);
    color: var(--color-text-secondary);
    font-family: monospace;
    font-size: var(--font-size-code);
    border-radius: var(--radius-btn);
    padding: var(--space-xs) var(--space-md);
    margin-top: var(--space-xs);
    width: 100%;
    overflow-x: auto;
    box-shadow: var(--shadow-1);
    cursor: pointer;
    transition: background-color 0.2s;
}
.code-block:active, .code-block:focus {
    background: var(--color-bg-btn-hover);
}
.note {
    background: var(--color-note-bg);
    color: var(--color-note-text);
    border-left: 0.25rem solid var(--color-text-accent);
    padding: 0.7rem 1.2rem;
    border-radius: var(--radius-btn);
    margin-top: 1.2rem;
    font-size: 1.02rem;
}
.references-section {
    margin-top: var(--space-xl);
    padding-top: var(--space-md);
    border-top: 0.0625rem solid var(--color-border);
}
.references-section h2 {
    color: var(--color-text-secondary);
}
.references-section ul {
    margin: 0.5rem 0 0 1.2rem;
}
.references-section a {
    color: var(--color-text-accent);
    text-decoration: underline;
    transition: color 0.2s;
}
.references-section a:hover {
    color: var(--color-text-secondary);
}

/* Custom Button */
.custom-btn {
    appearance: none;
    -webkit-appearance: none;
    background: var(--color-text-accent);
    color: #fff;
    border: none;
    border-radius: 0.5rem;
    padding: 0.7rem 1.5rem;
    font-size: 1.1rem;
    cursor: pointer;
    transition: background-color 0.2s;
}
.custom-btn:hover {
    background: var(--color-text-secondary);
}

/* Custom Checkbox */
.checkbox-label {
    position: relative;
    padding-left: 1.8rem;
    cursor: pointer;
    font-size: 1.05rem;
    user-select: none;
    display: flex;
    align-items: center;
}
.custom-checkbox {
    appearance: none;
    -webkit-appearance: none;
    width: 1.2rem;
    height: 1.2rem;
    border: 2px solid var(--color-text-accent);
    border-radius: 0.3rem;
    background: #fff;
    cursor: pointer;
    position: absolute;
    left: 0;
    top: calc(50% - 0.6rem);
    margin: 0;
}
.custom-checkbox:checked {
    background: var(--color-text-accent);
    border-color: var(--color-text-secondary);
}
.checkmark {
    display: inline-block;
    width: 1.2rem;
    height: 1.2rem;
    position: absolute;
    left: 0;
   top: calc(50% - 0.6rem);
    pointer-events: none;
}
.custom-checkbox:checked + .checkmark::after {
    content: '';
    display: block;
    width: 0.6rem;
    height: 0.6rem;
    background: #fff;
    border-radius: 0.15rem;
    position: absolute;
    left: 0.3rem;
    top: 0.3rem;
}

/* Custom Select */
.custom-select {
    appearance: none;
    -webkit-appearance: none;
    background: var(--color-bg-section);
    border: 2px solid var(--color-text-accent);
    border-radius: 0.5rem;
    padding: 0.7rem 2.2rem 0.7rem 1rem;
    font-size: 1.1rem;
    color: var(--color-text-secondary);
    background-image: url("data:image/svg+xml,%3Csvg width='16' height='10' viewBox='0 0 16 10' fill='none' xmlns='http://www.w3.org/2000/svg'%3E%3Cpath d='M2 2L8 8L14 2' stroke='%234f8cff' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 1rem center;
    background-size: 1.2rem;
    cursor: pointer;
}
@media (max-width: 56rem) {
    .appearance-main {
        padding: var(--space-lg) var(--space-md);
    }
    .example-grid {
        flex-direction: column;
        gap: var(--space-md);
    }
}