:root {
    --bg: #f5f5f5;
    --btn-bg: #e3e3e3;
    --btn-hover: #b0e0e6;
    --operation-color: #007f5f;
    --delete-color: #c1121f;
    --equal-bg: #38b000;
    --input-bg: #e3e3e3;
  }
  
  * {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  }
  
  body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: var(--bg);
  }
  
  .container {
    display: flex;
    flex-direction: column;
    width: 100%;
    max-width: 400px;
    height: auto;
    border: 1px solid #ccc;
    border-radius: 12px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
    background-color: white;
    padding: 16px;
  }
  
  @media (max-width: 600px) {
    .container {
      width: 90%;
    }
  }
  
  .display {
    height: 80px;
    margin-bottom: 16px;
    display: flex;
    align-items: center;
    padding: 0 10px;
  }
  
  input {
    width: 100%;
    height: 100%;
    background-color: var(--input-bg);
    border: none;
    text-align: right;
    font-size: 32px;
    padding: 10px;
    border-radius: 8px;
  }
  
  input:focus {
    outline: none;
    background-color: #e0e0e0;
  }
  
  .buttons-container {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    justify-content: center;
  }
  
  .buttons {
    flex: 1 0 21%;
    aspect-ratio: 1 / 1;
    border: none;
    border-radius: 50%;
    background-color: var(--btn-bg);
    font-size: 22px;
    cursor: pointer;
    transition: background-color 0.2s ease;
  }
  
  .buttons:hover {
    background-color: var(--btn-hover);
  }
  
  .operations {
    color: var(--operation-color);
    font-weight: bold;
    font-size: 24px;
  }
  
  .delete {
    color: var(--delete-color);
    font-weight: 600;
  }
  
  .equal {
    background-color: var(--equal-bg);
    color: white;
  }
  
  .line {
    background-color: #ccc;
    height: 1px;
    margin: 16px 0;
    width: 100%;
  }