body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
    background-color: #f4f7f9;
    color: #333;
}

.container {
    max-width: 800px;
    width: 90%;
    text-align: center;
    padding: 30px;
    border-radius: 12px;
    background-color: #ffffff;
    box-shadow: 0 8px 30px rgba(0, 0, 0, 0.1);
    border: 1px solid #ddd;
    margin: 20px;
}

h1 {
    margin-bottom: 10px;
    font-size: 2.2em;
    color: #2c3e50;
}

.description {
    color: #666;
    margin-bottom: 30px;
    line-height: 1.5;
}

/* Tools Hub Grid */
.tools-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 20px;
    margin-top: 20px;
}

.tool-card {
    background: #fff;
    border: 1px solid #e0e0e0;
    border-radius: 10px;
    padding: 20px;
    cursor: pointer;
    transition: all 0.3s ease;
    display: flex;
    flex-direction: column;
    align-items: center;
}

.tool-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 5px 15px rgba(0,0,0,0.1);
    border-color: #3498db;
}

.tool-icon {
    font-size: 2.2em;
    margin-bottom: 10px;
}

.tool-name {
    font-size: 1.1em;
    font-weight: bold;
    color: #2c3e50;
    margin-bottom: 5px;
}

.tool-desc {
    font-size: 0.85em;
    color: #7f8c8d;
}

/* Common Calculator Elements */
.calculator-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    gap: 15px;
    margin-bottom: 25px;
}

.nav-header {
    display: flex;
    margin-bottom: 15px;
}

.back-btn {
    background: none;
    border: none;
    color: #3498db;
    font-weight: bold;
    cursor: pointer;
}

.input-group {
    display: flex;
    flex-direction: column;
    text-align: left;
}

.input-group label {
    font-weight: bold;
    font-size: 0.9em;
    margin-bottom: 5px;
    color: #34495e;
}

.input-group input, .input-group select {
    padding: 10px;
    border: 1px solid #cbd5e0;
    border-radius: 6px;
    background-color: #f9fbfd;
}

/* Preset Buttons for Resistor */
.preset-buttons {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(60px, 1fr));
    gap: 5px;
}

.preset-buttons button {
    padding: 5px;
    font-size: 0.85em;
    cursor: pointer;
    background: #ecf0f1;
    border: 1px solid #bdc3c7;
    border-radius: 4px;
}

.resistor-section {
    text-align: left;
    margin-bottom: 20px;
    padding: 15px;
    background-color: #fcfdfe;
    border: 1px solid #edf2f7;
    border-radius: 8px;
}

.resistor-section h3 {
    margin-top: 0;
    margin-bottom: 15px;
    font-size: 1.1em;
    color: #4a5568;
    border-bottom: 2px solid #3498db;
    display: inline-block;
    padding-bottom: 3px;
}

hr {
    border: 0;
    height: 1px;
    background: #e2e8f0;
    margin: 25px 0;
}

.range-btn.active, .digit-btn.active, .r1-range-btn.active, .r1-digit-btn.active, .r2-range-btn.active, .r2-digit-btn.active {
    background-color: #3498db !important;
    color: white !important;
    border-color: #2980b9 !important;
}

.digit-grid {
    grid-template-columns: repeat(6, 1fr) !important;
}

@media (max-width: 600px) {
    .digit-grid {
        grid-template-columns: repeat(4, 1fr) !important;
    }
}

/* Result Box and Status */
.result-box {
    margin: 20px 0;
    padding: 15px;
    background-color: #f8f9fa;
    border-radius: 8px;
    border-left: 5px solid #3498db;
    text-align: left;
}

.result-box h3 {
    margin: 0;
    color: #2c3e50;
}

.status-tag {
    display: inline-block;
    padding: 5px 15px;
    border-radius: 20px;
    font-weight: bold;
    margin-top: 10px;
    text-transform: uppercase;
}

.status-pass {
    background-color: #2ecc71;
    color: white;
}

.status-fail {
    background-color: #e74c3c;
    color: white;
}

/* Formula Display Style (for KaTeX) */
.formula-display {
    background-color: #ffffff;
    padding: 15px;
    border-radius: 8px;
    margin-bottom: 25px;
    color: #2c3e50;
    border: 1px solid #e2e8f0;
    box-shadow: inset 0 2px 4px rgba(0,0,0,0.05);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 60px;
}

/* KaTeX specific tweaks */
.katex-display {
    margin: 0 !important;
}

/* Graph Container */
.graph-container {
    margin-top: 20px;
    background: #fff;
    border: 1px solid #ddd;
    border-radius: 8px;
    padding: 15px;
    overflow: hidden;
    box-shadow: 0 4px 6px rgba(0,0,0,0.05);
}

canvas {
    max-width: 100%;
    height: auto;
    display: block;
    margin: 0 auto;
}

.danger-btn {
    padding: 10px 20px;
    color: #fff;
    background-color: #e74c3c;
    border: none;
    border-radius: 6px;
    cursor: pointer;
}

@media (max-width: 480px) {
    .calculator-grid {
        grid-template-columns: 1fr;
    }
}