:root {
    /* Colors */
    --color-background: rgba(252, 252, 249, 1);
    --color-surface: rgba(255, 255, 253, 1);
    --color-text: rgba(19, 52, 59, 1);
    --color-text-secondary: rgba(98, 108, 113, 1);
    --color-primary: rgba(33, 128, 141, 1);
    --color-primary-hover: rgba(29, 116, 128, 1);
    --color-primary-active: rgba(26, 104, 115, 1);
    --color-secondary: rgba(94, 82, 64, 0.12);
    --color-secondary-hover: rgba(94, 82, 64, 0.2);
    --color-secondary-active: rgba(94, 82, 64, 0.25);
    --color-border: rgba(94, 82, 64, 0.2);
    --color-btn-primary-text: rgba(252, 252, 249, 1);
    --color-card-border: rgba(94, 82, 64, 0.12);
    --color-card-border-inner: rgba(94, 82, 64, 0.12);
    --color-error: rgba(192, 21, 47, 1);
    --color-success: rgba(33, 128, 141, 1);
    --color-warning: rgba(168, 75, 47, 1);
    --color-info: rgba(98, 108, 113, 1);
    --color-focus-ring: rgba(33, 128, 141, 0.4);
    --color-select-caret: rgba(19, 52, 59, 0.8);
    /* Common style patterns */
    --focus-ring: 0 0 0 3px var(--color-focus-ring);
    --focus-outline: 2px solid var(--color-primary);
    --status-bg-opacity: 0.15;
    --status-border-opacity: 0.25;
    --select-caret-light: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 24 24' fill='none' stroke='%23134252' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpolyline points='6 9 12 15 18 9'%3E%3C/polyline%3E%3C/svg%3E");
    --select-caret-dark: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 24 24' fill='none' stroke='%23f5f5f5' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpolyline points='6 9 12 15 18 9'%3E%3C/polyline%3E%3C/svg%3E");
    /* RGB versions for opacity control */
    --color-success-rgb: 33, 128, 141;
    --color-error-rgb: 192, 21, 47;
    --color-warning-rgb: 168, 75, 47;
    --color-info-rgb: 98, 108, 113;
    /* Typography */
    --font-family-base: "FKGroteskNeue", "Geist", "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    --font-family-mono: "Berkeley Mono", ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
    --font-size-sm: 12px;
    --font-size-base: 14px;
    --font-size-lg: 16px;
    --font-size-xl: 18px;
    --font-size-2xl: 20px;
    --font-size-3xl: 24px;
    --font-size-4xl: 30px;
    --font-weight-medium: 500;
    --font-weight-semibold: 550;
    --line-height-tight: 1.2;
    --line-height-normal: 1.5;
    --letter-spacing-tight: -0.01em;
    /* Spacing */
    --space-8: 8px;
    --space-12: 12px;
    --space-16: 16px;
    --space-24: 24px;
    --space-32: 32px;
    /* Border Radius */
    --radius-base: 8px;
    --radius-lg: 12px;
    /* Shadows */
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.04), 0 1px 2px rgba(0, 0, 0, 0.02);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.04), 0 2px 4px -1px rgba(0, 0, 0, 0.02);
    /* Animation */
    --duration-normal: 250ms;
    --ease-standard: cubic-bezier(0.16, 1, 0.3, 1);
}

/* Dark mode colors */
@media (prefers-color-scheme: dark) {
    :root {
        --color-background: rgb(13, 17, 23);
        --color-surface: rgb(38 46 52);
        --color-text: rgba(245, 245, 245, 1);
        --color-text-secondary: rgba(167, 169, 169, 0.7);
        --color-primary: rgb(166 193 219);
        --color-primary-hover: rgb(104 147 188);
        --color-primary-active: rgba(41, 150, 161, 1);
        --color-secondary: rgba(119, 124, 124, 0.15);
        --color-secondary-hover: rgba(119, 124, 124, 0.25);
        --color-secondary-active: rgba(119, 124, 124, 0.3);
        --color-border: rgba(119, 124, 124, 0.3);
        --color-error: rgba(255, 84, 89, 1);
        --color-success: rgba(50, 184, 198, 1);
        --color-warning: rgba(230, 129, 97, 1);
        --color-info: rgba(167, 169, 169, 1);
        --color-focus-ring: rgba(50, 184, 198, 0.4);
        --color-btn-primary-text: rgba(19, 52, 59, 1);
        --color-card-border: rgba(119, 124, 124, 0.2);
        --color-card-border-inner: rgba(119, 124, 124, 0.15);
        --color-select-caret: rgba(245, 245, 245, 0.8);
        --color-success-rgb: 50, 184, 198;
        --color-error-rgb: 255, 84, 89;
        --color-warning-rgb: 230, 129, 97;
        --color-info-rgb: 167, 169, 169;
    }
}

/* Base styles */
html {
    font-size: var(--font-size-base);
    font-family: var(--font-family-base);
    line-height: var(--line-height-normal);
    color: var(--color-text);
    background-color: var(--color-background);
    -webkit-font-smoothing: antialiased;
    box-sizing: border-box;
}

body {
    margin: 0;
    padding: 0;
}

*, *::before, *::after {
    box-sizing: inherit;
}

/* Typography */
h1, h2, h3, h4 {
    margin: 0;
    font-weight: var(--font-weight-semibold);
    line-height: var(--line-height-tight);
    color: var(--color-text);
    letter-spacing: var(--letter-spacing-tight);
}

h1 { font-size: var(--font-size-4xl); }
h2 { font-size: var(--font-size-3xl); }
h3 { font-size: var(--font-size-2xl); }
h4 { font-size: var(--font-size-xl); }
p { margin: 0 0 var(--space-16) 0; }
.mb-16 { margin-bottom: var(--space-16); }
.mt-16 { margin-top: var(--space-16); }
.mt-24 { margin-top: var(--space-24); }

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: var(--space-8) var(--space-16);
    border-radius: var(--radius-base);
    font-size: var(--font-size-base);
    font-weight: 500;
    line-height: 1.5;
    cursor: pointer;
    transition: all var(--duration-normal) var(--ease-standard);
    border: none;
    text-decoration: none;
    position: relative;
}
.btn:focus-visible { outline: none; box-shadow: var(--focus-ring); }
.btn--primary { background: var(--color-primary); color: var(--color-btn-primary-text); }
.btn--primary:hover { background: var(--color-primary-hover); }
.btn--primary:active { background: var(--color-primary-active); }
.btn--secondary { background: var(--color-secondary); color: var(--color-text); }
.btn--secondary:hover { background: var(--color-secondary-hover); }
.btn--secondary:active { background: var(--color-secondary-active); }
.btn--full-width { width: 100%; }

/* Form elements */
.form-control {
    display: block;
    width: 100%;
	max-width: fit-content;
    padding: var(--space-8) var(--space-12);
    font-size: var(--font-size-base);
    line-height: 1.5;
    color: var(--color-text);
    background-color: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius-base);
    transition: border-color var(--duration-fast) var(--ease-standard), box-shadow var(--duration-fast) var(--ease-standard);
}
select.form-control {
    -webkit-appearance: none;
    appearance: none;
    background-image: var(--select-caret-light);
    background-repeat: no-repeat;
    background-position: right var(--space-12) center;
    background-size: 16px;
    padding-right: var(--space-32);
}
@media (prefers-color-scheme: dark) { select.form-control { background-image: var(--select-caret-dark); } }
.form-control:focus { border-color: var(--color-primary); outline: var(--focus-outline); }
.form-label { display: block; margin-bottom: var(--space-8); font-weight: var(--font-weight-medium); font-size: var(--font-size-sm); }
.form-group { margin-bottom: var(--space-16); }
.font-mono { font-family: var(--font-family-mono); }

/* Card component */
.card {
    background-color: var(--color-surface);
    border-radius: var(--radius-lg);
    border: 1px solid var(--color-card-border);
    box-shadow: var(--shadow-sm);
    overflow: hidden;
    transition: box-shadow var(--duration-normal) var(--ease-standard);
}
.card:hover { box-shadow: var(--shadow-md); }
.card__body { padding: var(--space-24); }

/* Status indicators */
.status {
    display: inline-flex;
    align-items: center;
    padding: var(--space-8) var(--space-12);
    border-radius: var(--radius-base);
    font-weight: var(--font-weight-medium);
}
.status--error {
    background-color: rgba(var(--color-error-rgb), var(--status-bg-opacity));
    color: var(--color-error);
    border: 1px solid rgba(var(--color-error-rgb), var(--status-border-opacity));
}

/* Container layout */
.container {
    width: 100%;
    margin: 0 auto;
    padding: var(--space-16);
    max-width: 1024px;
}

/* General Layout */
.hidden { display: none; }
.header { text-align: center; margin-bottom: var(--space-32); padding: var(--space-32) 0; }
.header h1 { color: var(--color-primary); margin-bottom: var(--space-8); }
.subtitle { font-size: var(--font-size-lg); color: var(--color-text-secondary); margin: 0; }

/* Tab Navigation */
.tab-nav { display: flex; justify-content: center; margin-bottom: var(--space-32); border-bottom: 1px solid var(--color-border); }
.tab-btn { background: transparent; border: none; padding: var(--space-12) var(--space-24); font-size: var(--font-size-base); font-weight: var(--font-weight-medium); color: var(--color-text-secondary); cursor: pointer; transition: all var(--duration-normal) var(--ease-standard); border-bottom: 2px solid transparent; }
.tab-btn:hover { color: var(--color-primary); }
.tab-btn.active { color: var(--color-primary); border-bottom-color: var(--color-primary); }
.tab-btn:focus-visible { outline: var(--focus-outline); outline-offset: 2px; }

/* Tab Content */
.tab-content { display: none; }
.tab-content.active { display: block; animation: fadeIn var(--duration-normal) var(--ease-standard); }
@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }

/* Calculator Section */
.calculator-section { max-width: 800px; margin: 0 auto; }
.input-section { display: grid; grid-template-columns: 1fr 1fr; gap: var(--space-16); margin-bottom: var(--space-24); }
.input-section .btn { grid-column: span 2; justify-self: center; min-width: 150px; }
@media (max-width: 768px) {
    .input-section { grid-template-columns: 1fr; }
    .input-section .btn { grid-column: span 1; }
}

/* Results Display */
.results-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); gap: var(--space-16); }
.result-item { display: flex; justify-content: space-between; align-items: center; padding: var(--space-12); background: var(--color-secondary); border-radius: var(--radius-base); }
.result-label { font-weight: var(--font-weight-medium); color: var(--color-text); }
.result-value { font-family: var(--font-family-mono); font-weight: var(--font-weight-semibold); color: var(--color-primary); }
.method-steps { margin-top: var(--space-24); }
.step-item { margin-bottom: var(--space-16); padding: var(--space-16); background: var(--color-secondary); border-radius: var(--radius-base); border-left: 4px solid var(--color-primary); }
.step-title { font-weight: var(--font-weight-semibold); color: var(--color-primary); margin-bottom: var(--space-8); }
.binary-row { display: flex; align-items: center; margin-bottom: var(--space-8); font-family: var(--font-family-mono); font-size: var(--font-size-sm); }
.binary-label { min-width: 120px; font-weight: var(--font-weight-medium); }
.binary-value { color: var(--color-primary); letter-spacing: 1px; }

/* Practice Section */
.practice-section { max-width: 800px; margin: 0 auto; }
.practice-controls { display: grid; grid-template-columns: 1fr auto 1fr; align-items: center; gap: var(--space-16); margin-bottom: var(--space-24); }
.score-display { font-weight: var(--font-weight-semibold); color: var(--color-primary); text-align: right; }
.practice-problem { margin-top: var(--space-32); }
.problem-display { background: var(--color-secondary); padding: var(--space-16); border-radius: var(--radius-base); margin-bottom: var(--space-24); }
.problem-display p { margin: var(--space-8) 0; font-size: var(--font-size-lg); }
.practice-inputs { display: grid; grid-template-columns: repeat(auto-fit, minmax(250px, 1fr)); gap: var(--space-16); margin-bottom: var(--space-24); }

/* Feedback Section */
.feedback-item { display: flex; align-items: center; justify-content: space-between; padding: var(--space-12); margin-bottom: var(--space-8); border-radius: var(--radius-base); }
.feedback-correct { background: rgba(var(--color-success-rgb), 0.1); border-left: 4px solid var(--color-success); }
.feedback-incorrect { background: rgba(var(--color-error-rgb), 0.1); border-left: 4px solid var(--color-error); }
.feedback-info { background: rgba(var(--color-info-rgb), 0.1); border-left: 4px solid var(--color-info); }
.feedback-label { font-weight: var(--font-weight-medium); }
.feedback-user-answer { font-family: var(--font-family-mono); color: var(--color-error); }
.feedback-correct-answer { font-family: var(--font-family-mono); color: var(--color-success); }
.feedback-info .feedback-correct-answer { color: var(--color-primary); }

/* Reference Section */
.reference-section { max-width: 1000px; margin: 0 auto; }
.table-container { overflow-x: auto; }
.cidr-table { width: 100%; border-collapse: collapse; font-family: var(--font-family-mono); font-size: var(--font-size-sm); }
.cidr-table th, .cidr-table td { padding: var(--space-12); text-align: left; border-bottom: 1px solid var(--color-border); }
.cidr-table th { background: var(--color-secondary); font-weight: var(--font-weight-semibold); color: var(--color-text); }
.cidr-table tbody tr:hover { background: var(--color-secondary); }

/* Responsive Design */
@media (max-width: 768px) {
    .header h1 { font-size: var(--font-size-3xl); }
    .results-grid { grid-template-columns: 1fr; }
    .result-item { flex-direction: column; align-items: flex-start; gap: var(--space-8); }
    .practice-controls { flex-direction: column; align-items: stretch; }
    .practice-inputs { grid-template-columns: 1fr; }
}