body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: #f5f5f7;
    color: #1d1d1f;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
}

.container {
    background-color: #ffffff;
    padding: 40px;
    border-radius: 18px;
    box-shadow: 0 4px 12px rgba(0,0,0,0.08);
    width: 100%;
    max-width: 500px;
}

h1 {
    font-size: 28px;
    font-weight: 600;
    text-align: center;
    margin-bottom: 30px;
}

h2 {
    font-size: 22px;
    font-weight: 600;
    border-bottom: 1px solid #e5e5e5;
    padding-bottom: 10px;
    margin-bottom: 20px;
}

.calculator {
    margin-bottom: 40px;
}

.calculator:last-child {
    margin-bottom: 0;
}

.input-group {
    margin-bottom: 15px;
    display: flex;
    flex-direction: column;
}

.input-group label {
    font-size: 14px;
    font-weight: 500;
    margin-bottom: 5px;
    color: #6e6e73;
}

input[type="number"], select {
    width: 100%;
    padding: 12px;
    border: 1px solid #d2d2d7;
    border-radius: 8px;
    font-size: 16px;
    box-sizing: border-box;
    background-color: #f5f5f7;
    color: #1d1d1f;
}

input[type="number"]:focus, select:focus {
    outline: none;
    border-color: #007aff;
    box-shadow: 0 0 0 2px rgba(0,122,255,0.2);
}

button {
    width: 100%;
    padding: 14px;
    border: none;
    border-radius: 8px;
    background-color: #007aff;
    color: white;
    font-size: 17px;
    font-weight: 600;
    cursor: pointer;
    transition: background-color 0.2s;
}

button:hover {
    background-color: #005ec4;
}

.result {
    margin-top: 20px;
    padding: 15px;
    border-radius: 8px;
    background-color: #f5f5f7;
    font-size: 18px;
    font-weight: 500;
    text-align: center;
    min-height: 24px;
    transition: background-color 0.3s ease, color 0.3s ease;
}

.result.success {
    background-color: #e5f7ed;
    color: #00843d;
}

.result.error {
    background-color: #fdeeee;
    color: #c42e2e;
}

.percentage-calculator-form .input-group {
    flex-direction: row;
    align-items: center;
    gap: 10px;
}

.percentage-calculator-form .percent-input {
    width: 100px;
}
.percentage-calculator-form select {
    flex-grow: 1;
}

.percentage-modes {
    margin-bottom: 20px;
    display: flex;
    flex-wrap: wrap;
    gap: 15px;
}

.percentage-modes label {
    display: flex;
    align-items: center;
    cursor: pointer;
    font-size: 14px;
}

.percentage-modes input[type="radio"] {
    margin-right: 8px;
}

.percentage-form {
    margin-bottom: 15px;
}

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

.input-group-inline label {
    font-size: 16px;
}

.input-group-inline input[type="number"] {
    width: 120px;
    text-align: center;
}

.percentage-modes h4 {
    margin-bottom: 10px;
}
.percentage-modes p {
    margin: 5px 0;
}

#percentage-operation {
    -webkit-appearance: none;
    -moz-appearance: none;
    appearance: none;
    background-image: url("data:image/svg+xml;charset=US-ASCII,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20width%3D%22292.4%22%20height%3D%22292.4%22%3E%3Cpath%20fill%3D%22%23007AFF%22%20d%3D%22M287%2069.4a17.6%2017.6%200%200%200-13-5.4H18.4c-5%200-9.3%201.8-12.9%205.4A17.6%2017.6%200%200%200%200%2082.2c0%205%201.8%209.3%205.4%2012.9l128%20127.9c3.6%203.6%207.8%205.4%2012.8%205.4s9.2-1.8%2012.8-5.4L287%2095c3.5-3.5%205.4-7.8%205.4-12.8%200-5-1.9-9.2-5.4-12.8z%22%2F%3E%3C%2Fsvg%3E");
    background-repeat: no-repeat;
    background-position: right 10px top 50%;
    background-size: .65em auto;
    padding-right: 30px;
}