:root {
        --main: #1999c6;
        --bg: #f7fbfe;
      }
      html,
      body {
        margin: 0;
        padding: 0;
        background: var(--bg);
      }
      body {
        font-family: "Segoe UI", Arial, sans-serif;
        color: #234;
      }
      .container {
        max-width: 390px;
        margin: 38px auto 0 auto;
        background: #fff;
        border-radius: 18px;
        box-shadow: 0 4px 22px #1999c61a;
        padding: 25px 14px 22px 14px;
      }
      .title {
        text-align: center;
        font-size: 1.15em;
        color: var(--main);
        font-weight: bold;
        margin-bottom: 12px;
      }
      .form-row {
        display: flex;
        flex-direction: column;
        gap: 5px;
        margin-bottom: 15px;
      }
      .form-row label {
        font-size: 1em;
        color: #147399;
        font-weight: 500;
      }
      .form-row input[type="datetime-local"] {
        box-sizing: border-box;
        padding: 10px 10px;
        border-radius: 7px;
        border: 1.2px solid #aee3f7;
        font-size: 1.08em;
        width: 100%;
        background: #fafdff;
        color: #234;
        transition: border 0.15s;
      }
      .form-row input[type="datetime-local"]:focus {
        border-color: var(--main);
      }
      .result,
      .countdown {
        background: #e2f5fc;
        border-radius: 12px;
        color: #15748d;
        font-size: 1.08em;
        padding: 13px 11px 11px 11px;
        text-align: center;
        margin-bottom: 9px;
        min-height: 38px;
        font-weight: 500;
        word-break: break-word;
      }
      .countdown {
        background: #f7ebff;
        color: #954fc9;
        margin-top: 5px;
        margin-bottom: 5px;
      }
      .footer {
        color: #789;
        text-align: center;
        font-size: 0.93em;
        margin-top: 15px;
      }
      #backBtn {
        position: fixed;
        left: 50%;
        bottom: 32px;
        transform: translateX(-50%);
        background: #1999c6;
        color: #fff;
        font-weight: 700;
        border: none;
        border-radius: 2rem;
        padding: 0.58em 1.5em;
        box-shadow: 0 4px 16px #1999c633;
        font-size: 1.09em;
        text-decoration: none;
        cursor: pointer;
        letter-spacing: 0.01em;
        transition:
          background 0.15s,
          transform 0.12s;
        z-index: 2000;
      }
      #backBtn:hover {
        background: #106d92;
        transform: translateX(-50%) scale(1.04);
      }
      @media (max-width: 500px) {
        .container {
          max-width: 98vw;
          padding: 10px 2vw 10px 2vw;
        }
        #backBtn {
          bottom: 18px;
          font-size: 0.98em;
          padding: 0.48em 1em;
        }
      }