body {
    font-family: Arial, sans-serif;
    background-color: #f0f0f0;
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
  }
  
  .container {
    background-color: #ffffff;
    padding: 20px;
    border-radius: 5px;
    box-shadow: 0px 2px 5px rgba(0, 0, 0, 0.1);
    max-width: 500px;
    width: 100%;
  }
  
  h1 {
    text-align: center;
    margin-bottom: 20px;
  }
  
  .converter {
    display: flex;
    justify-content: space-between;
    flex-wrap: wrap;
    align-items: center;
  }
  
  input, select, button {
    padding: 10px;
    border: 1px solid #cccccc;
    border-radius: 5px;
    margin-bottom: 10px;
    width: 100%;
  }
  
  .select-wrapper {
    position: relative;
    width: 48%;
}

select {
appearance: none;
width: 100%;
background-image: url('data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 4 5"><path d="M2 3.5L.6 1h2.8L2 3.5z"/></svg>');
background-repeat: no-repeat;
background-position: right .7em top 50%;
padding-right: 1.5em;
}

button {
background-color: #4CAF50;
color: white;
cursor: pointer;
transition: background-color 0.3s;
}

button:hover {
background-color: #45a049;
}

.swap {
background: none;
border: none;
font-size: 1.5em;
cursor: pointer;
}

.output, .error {
text-align: center;
font-size: 1.5em;
margin-top: 10px;
}

.error {
color: red;
display: none;
}